well, you will probably not find a voodoo5 6000 at a fleamarket or thriftstore so prices on those rare items will always be high. But an awe32 or awe64 (gold)?
These are VERY common cards and can still be found for next to nothing. Just get out there and search for the stuff (finding it is most of the fun anyway!!).
I never use ebay because prices are just to high (and/or shipping is). After searching for a few years i too will pay a little extra for items that are just hard to find and i really want but nothing extreme.
I have a few awe32 cards and i didn't pay more than just a few euro or next to nothing in a package deal. Same thing for my sb pro and sounblaster pro2.
Now, if you are into boxed/sealed items it is a different story but when it comes to normal useable hardware i don't see the extreme value just because there are only a couple on ebay now.
I don't get it when people for example pay 50 dollars or so for a voodoo2 card when there are thousands still out there.
Popular items like v1/v2/v3 cards, asus p2b/p3b-f boards, isa soundblasters, socket7 stuff are often found in package deals for very little money since people are still cleaning out their garages or whatever.
asus tx97-e, 233mmx, voodoo1, s3 virge ,sb16
asus p5a, k6-3+ @ 550mhz, voodoo2 12mb sli, gf2 gts, awe32
asus p3b-f, p3-700, voodoo3 3500TV agp, awe64
asus tusl2-c, p3-S 1,4ghz, voodoo5 5500, live!
asus a7n8x DL, barton cpu, 6800ultra, Voodoo3 pci, audigy1