Like I discussed long ago, the problems you're having with that 4650 are because of the weird setup of the card itself, not the drivers. The AGP version of the 4650/70 uses a bridge chip and requires special drivers provided by the card manufacturer itself, ATI/AMD never supported such a configuration with the 46x0 GPU. I have a regular HD4650 PCIe card and have never had issues with it in either Windows XP or 7 over a range of driver versions.
I definitely know you aren't getting AGP 1x/2x cards installed in your motherboard because they won't fit in the slot. AGP 1x/2x is keyed differently from AGP 4x/8x. There are universal key cards with notches to work in both slot types, so those can technically work. If you have universal AGP cards that aren't working, try cleaning the edge connector on the card. I was playing with some of my old AGP cards the last couple of days and several of them didn't work at all until I cleaned the connectors with deoxit gold. One of them was so bad I had to resort to a pencil eraser.
I definitely sympathize with you on the astronomical cost of AGP cards these days. The world has gotten vintage computer fever thanks to various Youtubers and drove costs of old gear way up. I'm glad that I kept most of my old gear over the years because I definitely wouldn't be able to afford it today.