Depends on the model, and the condition. A new-in-pouch Mk. VI might run $650-$750, while a well-used Mk. I might fetch $450. I bought an unfired Mk. I last year for $550, and I've seen nice, used ones for more than that. In my experience, the matte stainless Mk. V is the most common variation, and a nice one should go for $500-$600.