Answer by NobodysNightmare for Regular expression - only digits, dots,commas and first character should be $

My proposal (untested):

\$(\d{1,3})(,\d{3})*(\.\d+)?

we require a dollar, followed by a up to 3 digits.

then there might come more exactly 3-digit long groups.

at the end there might be a comma followed by at least one digit (or no comma and no digits)