Start at $1000 and go up to $1500. Any more than that, and I would consider buying new. Good luck.
If you want wifi, it may not work on that particular controller and you may have to buy a new controller in addition to the wifi adapter. Just want to make sure you know it ahead of time in case that was a key interest of yours.
I would also find out the serial number and other accessories that may already be on it. Some current accessories are not available below a certain serial number. MAK does a pretty good job in their product descriptions of explaining what serial numbers accessories are made for use in.