My good one cost me $2,800.
The one I have converted to a camper cost me $1,200 (from the auctions).
In my opinion, they are worth around $3,000 depending on condition. If it was in good unmodified condition, I'd consider paying $4,000. If it needed a fair bit of work, well, some bits can be costly. For example, the hitch is about $250. Then you will need to pay an engineering company to modify it for the brake connection bracket.