If you're looking for absolutely dirt cheap cards that will show the textures, newegg has some SiS cards that are marked as DirectX8 compliant (still below the game's specs, but should show the textures) for around $20. The cheapest DirectX9 card would be GeForce FX 5200, at around $30.

Note however that both of those cards will, while supporting more advanced graphic features and thus looking nicer, provide consdierably poorer performance vs the GeForce2 Ultra (which while old was a very powerful card in its day). If you want to find a card that is both DirectX9 compliant and that won't be as much a downgrade as it is an upgrade, a Radeon 9600XT is the cheapest card with a comparable fillrate. Those run around $65. I used one myself until just recently and depending on the rest of your system, it will run GC2 flawlessly.

I have a couple of old computers like that (AGP 4x). They're quite obsolete. The computer I normally use is up-to-date and runs a GeForce 7900. If you want to switch to PCIe, you're going to need a whole system (motherboard, processor, memory, power supply, video card). It's not an inexpensive transition. However, I think you might be able to get something like a GeForce 6800 AGP to run in 4x mode. IIRC, I tried a 6800 on one of my old Athlon T-Bird computers and it worked. Those cards are pretty cheap on eBay.

I've looked up your motherboard, and it only supports up to AGP 4x. Even AGP 8x is considered obsolete, so you might have trouble finding a video card that old.

There are still plenty of AGP cards out there, just not high-end ones (and the mid-end is quickly eroding). But most any AGP 8x card will generally be compatible with AGP 4x as well, it just won't be as fast as it could be.