Start with flea-bay. There will be plenty of choice but as always the more you spand the better you get.
If you just want a toy then that's fair money for something with life left in it and a decent chance of being roadworthy for the foreseeable future too.
A little bit more should get you a decent late model with a few comforts, but why bother if you are going to off-road it?
Try the wanted, try our for sale, try Autotrader.
Don't buy the first one you see but always take cash. Be prepared to walk away if it's not right, if it is kick the seller in the nuts, then be prepared to haggle.
It's a buyer's market, the a**e has fallen out of used 4x4 this year.
Good luck.