The going price around here depends a lot on the condition of the cutter, as you might expect. Five-foot cutters are the most common by far. For a five foot cutter, you can see asking prices around $450-$600 if the cutter is in excellent condition. I mean, very little to zero rust, paint is intact, etc... Not exactly "nearly new" maybe, but close. Once you get to what I would call "used but still good" condition, they run closer to $300-$400. In this condition, there is some surface rust, you can still see the paint, maybe some small areas that are rusted through, and the unit is definitely dinged up, but still basically in shape. Finally, you can find some in the $200-$300 range. These are "on their last legs". They are probably totally rust covered and may be beat to heck. There are still some good values in that range, but you have to be really careful.
Personally, I can't imagine spending money on one in the $450+ price range. There are a lot of gems to be found in the $300-$400 price range with cosmetic damage only. Unless you just really want a new cutter to put the dings in it yourself, or you need something that you're having trouble finding used, like a larger size or a heavy-duty instead of standard-duty.