I'd just change it a little bit:

/^\$?\d+(\.\d\d)?$/

That matches $12, $12.00, $0.12, etc.., but not $12., $.50, $12.013, etc..

Regards, octopus
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GED/CC d-- s:- a--- C++(+++) UL+++ P++++$ L++>++++ E--- W+++@ N o? K? w-- O- M-(+) V? !PS !PE !Y PGP+(++) t-- 5 X+ R+(+++) tv+(++) b++@ DI+() D+ G++ e->+++ h!++ r+(++) y+