They don't seem to be too expensive on ebay. I see a few used FW900 and 2070SB units for under $200. However, the quality on these things is highly variable, and getting a local pickup is necessary to avoid further problems from shipping damage. There used to be some ebay sellers that had many of them available and allowed you to drive to their warhouse and pick the one you wanted, but I don't see them anymore. If you buy blindly and get it shipped, I would say you have about a 70% chance of getting one that is defective or broken in some way, and that includes brand new ones if you somehow manage to find one of those.
I tell people who already have a good one to hang on to it as there is nothing else that touches them for gaming (LCDs have basically stopped improving since 2006, with cheap, low end ones increasingly dominating the market, and computer OLED displays are still at least two years off), but otherwise it's a huge hassle to get one and is not worth it.