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Regex Pattern to Validate Text Input With Max Value and Max Decimal Place

I need to create a pattern for a "text" type input to only allow a number from 0 to a specific max value and at the same time and validate to a specific number of decimal places.
Quick example:
Max Value = 300.86
Max Decimal Places = 3
Valid inputs:
0
1
300
300.86
300.85
300.850
300.851
.2
0.3333
Invalid inputs:
-1
301
300.87
300.861
1,30.2
1,.0
,.1
Currently I only know how to validate number of decimal places using this pattern:
^[,0-9]*(.\d{1,{0}})?$
Note:
I can't use type=number because I can't use any pattern with that :(
please help

I think something like this, is what you're after:
^(300(?:\.(?:[0-7]\d{0,2}|8(?:[0-5]\d?|60?)?))?|[0-2]?\d{0,2}(?:\.\d{0,3})?)$
See it here at REGEX STORM.
(Had to tweak it there, to end in \r, because REGEX STORM wouldn't match $ with end of line even though multi-line was selected???)
Explanation
It has two parts. The latter [0-2]?\d{0,2}(?:\.\d{0,3})? test for numbers below 300. It optionally starts with 0, 1 or 2 ([0-2]?). Then any two digits can follow (\d{0,2}). Then, optionally, it's followed by a . which, if present, can be followed by up to three digits (decimals) ((?:\.\d{0,3})?).
The first part - 300(?:\.(?:[0-7]\d{0,2}|8(?:[0-5]\d?|60?)?))? - test for when the integer part is exactly 300. It may then optionally be followed by a decimal point, and one out of three cases:
[0-7]\d{0,2} a digit in the range 0 to 7, followed by up to two digits
8(?:[0-5]\d*|60*)? an 8 followed by a digit in the range 0 to 5, optionally followed by a digit (The [0-5]\d? alternation).
or the number 86 and an optionall 0 (the 60? alternation)
These parts are in a capturing group separated by an alternation - |. The whole expression must be at the start of the string (^) (or line with multi-line flag) and at the end of the same ($).
Edit
Done some tweaking 'cause some numbers wrongly failed.
Edit 2
Completely missed "the maximum number of decimals" part. Fixed. (Fooled by the "valid" example 0.3333)

I don't know anything about C# so I'll just have to assume that what I can do in Python, you can find some way to do in C#. I'll give you my suggestion in pseudocode (this is not meant to mirror Python).
maxValue = some number
nDecimals = some number
givenValue = text with some number to be tested
#split number on decimal; remove non-digit characters from each side
leftSideOfDecimal = Replace(pattern = '^(\d{1,3}(,\d{3})*)(\.\d*)$', replacement = '\1', givenValue)
leftSideOfDecimal = Replace(',', '', leftSideOfDecimal)
rightSideOfDecimal = Replace('^(\d{1,3}(,\d{3})*)(\.\d*)$', '\3', givenValue)
rightSideOfDecimal = Replace('\.','',rightSideOfDecimal)
leftSideOfDecimal = pass leftSideOfDecimal to function to change type from text to integer
if leftSideOfDecimal <= maxValue and numberOfCharacters(rightSideOfDecimal) == nDecimals:
do whatever you want
Alternatively, if you have a function by which you can split strings on a given character (like a decimal or comma), then you just split the input on the decimal, clean up the first side as in the code, and then proceed with the last three lines of the code above. That way would save you from having to use a mildly complicated regex.

Regex validator not working as expected

Updated
I need to validate numbers, with decimal separator as , (comma) but this is not working:
validate.ValidationExpression = #"^[1-9]\d*(,\d+)?$";
123,01; 0,01; 0,001; 123456789,01 these are the numbers I would like to allow
Any help will be appreciated.

How about this:
^\d+(,\d+)?$
Visual explanation:
http://www.regexper.com/#%5E%5Cd%2B(%2C%5Cd%2B)%3F%24
That will:
^ Start at the beginning of a line
\d+ Find at least one, but as many as possible digits
( Start of a group
, The decimal sign
\d+ Find at least one, but as many as possible digits
) End of the group
? Makes the entire group optional
$ End of the line
This should capture integers and decimal numbers alike.
Try it out here:
http://regexr.com/398q6

That should do the work
^[-+]?[0-9]*,?[0-9]+$
It validates all of your examples and it supports negative numbers and numbers without any floating part.

If you want all your numbers to be accepted (123,01; 0,01; 0,001; 123456789,01) you have to change the first number 1 to 0, like this:
validate.ValidationExpression = #"^[0-9]\d*(,\d+)?$";
since you are basicly saying that any number 1-9 followed by , and 0-9 are fine so it wont select the ones that has a 0 before the ,.

validate.ValidationExpression = #"^\d+[,]?\d*$";
this will accept both 90 and 90,000

Discount mask with regex

Is it possible to create a 'dynamic' discount mask that takes % or numbers as discount values? What is the simple way to do this?
the samples of valide input: -25% or 0.25 or -5$ not 0 and two digit after dot

Try
#"(\+|-)?(\d+(\.\d*)?|\.\d+)%?"
It will find:
123.23
12.4%
.34
.34%
45.
45.%
8
7%
34
34%
+2.55%
-1.75%
UPDATE
and with ...
#"(\+|-)?(\d+(,\d{3})*(?!\d)(\.\d*)?|\.\d+)%?"
... you can include thousands separators as well.
I must confess that my second regex expression looks like a cat had walked accross my keyboard. Here the explanation
(\+|-)? optionally ? a plus or a minus sign.
\d+(,\d{3})*(?!\d)(\.\d*)? one or more digits \d+ followed by any number of thousands separators plus three digits (,\d{3})*, not followed by any digit (?!\d) in order to disallow four digits in sequence, optionally followed by a decimal point and any number of digits (\.\d*)?.
|\.\d+ or alternatively a decimal point followed by at least one digit.
%? finally an optional percent sign.

If I understand your question right, you want something like this:
#"^[+-]?(?:\d*\.)?\d+[%$]?$"
That's partly based on your example of -5$. Usually, though, the $ would go in front, so you'd want something like:
#"^(?:\$(?!.*%))?[+-]?(?:\d*\.)?\d+%?$"
That would allow $-5.00, 10, or +20%, but block $5%.
Edit:
Running with Olivier's idea of allowing commas:
#"^(\$(?!.*%))?[+-]?(\d{1,3}((,\d{3})*|\d*))?(\.\d+)?\b%?$"
Expanded to make it easier to understand:
#"^ #Require matching from the beginning of the line
(\$(?!.*%))? #Optionally allow a $ here, but only if there's no % later on.
[+-]? #Optionally allow + or - at the beginning
(
\d{1,3} #Covers the first three numerals
((,\d{3})*|\d*) #Allow numbers in 1,234,567 format, or simply a long string of numerals with no commas
)? #Allow for a decimal with no leading digits
(\.\d+)? #Optionally allow a period, but only with numerals behind it
\b #Word break (a sneaky way to require at least one numeral before this position, thus preventing an empty string)
%? #Optionally allow %
$" #End of line

Regular Expression for float and percentage

I need regex patterns for floating point numbers with optional % sign at the end like
12.32
12.32%
0.32
.32
.32%
arbitrary length of numbers on left and right of floating point numbers. I need this to validate input in asp.net mvc app
UPDATE:
forgot following combinations
12%
35
45%

This regex should do it for you...
\d*\.\d+%?
Which means... zero or more digits (\d*) followed by a period (escaped \.) followed by one or more digits (\d+) followed by an optional % (%?)
Update: match whole numbers
\d*\.?\d+%?

\d*\.\d{1,}%?
This matches all your cases.
ADD:
I answered the question in the comment about the {1,}: since I wasn't sure if single digit after the decimal point would be a valid input for you (all your examples have at least 2 digits after the point) I didn't use the plus-notation but rather indicated the number of digits explicitly. Here the first number indicates the minimal and the second number (omitted here) the maximal number of the digits after the point. If you want that all your input values have at least 2 digits after the point, use {2,} instead of {1,}.

need a regex for a positive max 2 digits after . floating number

Hi
I need a C# regex for a positive floatin no with maximum 2 digits for decimals. Also the regex should check for letters and alphanumerical chars (not allow them) and not allow also the input value to be empty (0 characters).
Thanks

^[+]?[0-9]+([.][0-9]{1,2})?$
This will force it to have either a + or nothing at the start, followed by at least 1 number, then optional (decimal followed by 1 or 2 numbers)
For others, yes, I know of \d, :digit:, using \., etc. I just prefer using [0-9] and [.], it makes them stand out easier for me.