If it works in Vista/7 I'm sure it will work in 8 as well. I just traded for a GTX 295. The 295 is roughly in the same camp as the X2 performance wise. Supports DX 10 and is limited to a 1GB buffer.
I did see another GTX for sale here for $95.00. So I suppose in the ~100 dollar range depending on if you have the original box and accessories might fetch a little more. These cards are still formidable in DX 9/10. I think if someone wants to put together a cheap gaming rig there is interest.
My reason for trading is I wanted to explore Physx without investing much in another card. Others will want or not an X2 for their own reasons. But I think there is a healthy market for good used parts. Even older stuff. There is a certain fun factor with buying stuff just to mess around with the hardware imo.