Since I don't what people are asking for on ebay is "fair" or accurate, I just wanted to hear your expert opinions  :)
Oh and how do prices differ between AGP and PCI?

An agp voodoo2 is extremely rare and last time I saw it on ebay, it sold for more than $300 USD. Theres a bunch of brand new voodoo 2 from russia going for about $50 each including shipping. I won two auctions for two matching pairs for about 30 each.
I put up a pair of diamond monster voodoo2 on ebay  for about 60 a few weeks ago, and it sold very quick! It's crazy to think that these things are still somewhat in demand, but if you keep a close eye on ebay, you might be able to grab one or two for about 15-30 each. Timing has to be right though, but they're out there!

Queso explained very good the situation, I only want to add one more thing: it depends a lot if the card is bulk/bare or if it has the original box and accessories. Bulk cards are cheap, VGA cables are also cheap and common, SLI cables are harder to find, but they aren't expensive. But full boxed cards can get very expensive.

Also the model of the card is important. Bulk Voodoo2 cards made by Diamond or Creative are quite easy to find and aren't very expensive. Other brands (Hercules or Gainward for example) are harder to find and they are usually more expensive. Some exotic brands are very hard to find and they are quite expensive.

I remember selling sealed NOS 8MB OEM cards for 2 EUR each about 10 years ago ... (which was cheap back then).  I had 60 cards which would made a nice profit for 15 EUR each these days ;-).

As stated by others it depends a lot on the brand, condition and accessoires. Especially boxed version sell for decent prices :).

Yea, the box makes a huge difference...I was bidding on the mint hercules voodoo 2 that had everything included, but gave up when it passed 150. It sold for 250 shipped! Let's not even think about the obsidian x-24, That thing sold once (a few months ago) for 600+. :o No thanks! haha

Yeah I figured things gone up!.. Well since I'm not much of a collector and more of a user, I will probably aim for diamond monster voodoo2 :) Hey are they actually making new cards in Russia? :o

An unboxed one will indeed be the cheapest way to go. I think some people got a hold of "new old stock" somehow. They seem to never have been used because mine arrived minty fresh with no scratches on the pci connector.