Translations:Using regular expressions/128/en
From LimeSurvey Manual
It forces two decimal points and accepts numbers from 1.00 to 999,999,999.00 with an optional comma delimiting thousands/millions including all of the following: 1.00, 1,000.00, 12,345.67, 12345,02, 123,456,468.00, 1234566.00, 123456789.00 but not 1,23.00, 12,3.4 or 1234,43.04
/^[1-9][0-9]{0,2}(?:,?[0-9]{3}){0,3}\.[0-9]{2}$/
Similar to the above: Forces two decimal points but accepts a "0" before decimal separator ",".
/[0-9]{0,2}(?:,?[0-9]{3}){0,3}\.[0-9]{2}$/