Is it V1, V2 or V3? (What letter does it say after the bios version on power up, A, B or C?)
If its a V3, does it have the "freeze mod" done on it?
I bought one about a year ago for just over $100 + shipping (V3, with freeze mod).
I've modded mine to use a compact flash now instead of a HD. (needs a bios update).
I'd probably pay more for a z64 in its original state than in the PC case. The nice thing about the Z64 is that it was moulded to match the N64.