Gf4MX cost around 4000 on Ritchie Street, last I heard. That's a li'l too much to spend on a PCI card if u ask me. U cld probably get a new mobo as some1 suggested. U cld then get an FX 5200 AGP for just rnd 2-2.5K (definitely not more). If u don't wanna wait that long u can go for the MX, if u don't mind the 500 extra bux. Of course it's your choice ultimately.
After an extensive search (for myself) all I could find for a lower price was a SiS 32MB PCI card (315 chipset based) for 2150. It's equivalent to a GeForce 2, well just about. But it can't spell the p of pixel shading. So u can't play DIII and all that. But relatively undemanding games like PoP, Fifa 2k5, NFS UG (1&2) will work. HL2 should work methinx, if the rest of ur system is capable enuf. Of course u can't play hotter games like CoD, Splinter Cell, etc.