Hey Todd, you may have an easier time finding a used PCI video card than a AGP card. AGP cards also come in different flavors, not all AGP equipped computers will support all flavors of AGP.
Are there any computer repair shops near you? A decent one will probably have a box of used video cards that they'll sell cheap.
If no one can help you out, check this one out at Newegg.com:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814143032 It's $20 + shipping. It's out of stock right now, but has an ETA of 3/9, so they should have them within a couple days.
I have some used PCI Express cards, but no PCI or AGP.
-Michael