Since your motherboard
limits you to AGP you are kinda limited on choices.
It looks like, for right around $100, your best bet is something like this Evga 7600 GT
at $107 pre-rebate, $87 post rebate.
An ATi x1650XT
is pretty close at $95.
Be aware that neither is a really good card, particularly on AGP, so don't expect overwhelming performance. You should be able to squeeze 1280x1024 at 'balanced' settings out of either though I'd think.
(I have no clue what that GPU you have is.)