Yup, Rich is right on. A new one would sell for more than its weight in gold. Used ones you take a gamble with.
There is an option that will cost about the same as getting a used one. A user here (dang, keep forgetting his screen name) makes a kit to convert to the newer style HIDs. Those HIDs are cheap and plentiful and standard, unlike the Mark. Costs about $200 and included two new ballasts, capsules and adapters.