This should work for you:
"^\d{1,3}(\.\d{3})*,\d{1,2}$"
It matches a number ending with comma followed by one or two digits:
",\d{1,2}", having optional digit triplets separated by a 'dot' thousands separator:
"(\.\d{3})*" and starting with one to three digits:
"^\d{1,3}".
If you want an optional fraction part, use
"(,\d{1,2}){0,1}$" instead of
",\d{1,2}".