The reality is when you go to a store there's only going to be a limited selection of AGP, cuz the preferred PCI-express format has been out for a long time now. So you should prob'ly go and see what they have, then do some look-up.
More generally, a question like "best cheap ___" is one where there's no single good answer. One man's cheap might be another man's expensive.
Tom's Hardware benchtests graphics cards and makes rankings of video cards so you can see where a particular card at a particular price point falls relative to its peers.
hope this helps
what is the best cheap video card on an AGP 8X?