Gotta be the absolute worst time in the history of the world to ask that question.  New truck prices are through the roof, so people can only afford used.  And people are using their Covid checks to buy used cars & trucks  

I’d look for a 2-wheel drive truck with body damage. Or a fixer that you know how to repair yourself. Otherwise I’d cross my fingers and hope  prices correct in the next few months.

The used market is the worst it’s been ever. And it’s going to stay that way. Although, the best you may be able to find around 5k is early 90s gas Fords or Chevs most will be rusted out but you might get lucky and find someone who babied the truck. Important question what are you going to use this truck for? 

The 2000-2006 tundra access cab sr5 are really cheap and are great work trucks and fit your price range. 

If you could find an old Toyota that would be great. You might even to find a good ranger. Just realize it will not last as long as the Toyota.