If the x1800s are still kind of pricey, you might want to consider one of x800/850’s. All are older cards and many are charging way too much for them but on the 1800’s or the 800/850’s there are occational great bargains to be found. I almost got an x850 xt for 100$ locally (half price) but found that the 2600xt was a better deal for me (because it was for an htpc, its not a beter card overall). That was a few months ago anyway (a lot can change in that time).
I’m no expert on video cards (in fact I like to research all my purchases well but I despise shopping for vid cards, and run older cards due to the frustration of shopping for them), but here is a chart that gives you general overall performance comparisions of most cards (the higher on the list it is, there better overall averaged performance is).
I would use this as a very basic guideline if you are confused by the billion models out there and have no idea how they compare. Once you have narrowed down a few models you like, research them more to see if they fit your needs. Be aware that the extentions (gt etc), and factors like memory speed (ddr2/3/4, 64bit, 128bit, 256 bit) may or may not make a huge diffrence on the same model card (thats why I say, when you narrow it down, research further).
I know that didn’t help a lot (like I said, I’m not a video card expert, in fact I try to avoid shopping for them), but hopefully it helped a little.