For <$70 (US) you can pick up an nVidia 8500GT powered card, 256MB, DVI out, etc. Decent card, supports DX10, OGL 2.0, SLI.
Any of the component manufacturers like XFX, MSI, Visiontek, Gigabyte, etc.
Of course you can keep upgrading incrementally, a 8600 will be a little more $/a little faster, 8800, etc., but those cards in the $100-200 range I believe. Moderate rez, a few more exotic features turned down and you should be in decent shape.
If you can swing it, maybe try to squeeze in a 8600GT, faster memory, decent overclocker, should be able to score the 256MB model < $100.
I'd shop www.newegg.com or www.mwave.com - used them both for several years with outstanding success (MWave even replaced some one year old components NQA, and just took back for full credit our Netgear Powerline without the complete packaging for a full credit).