Go old school!
79 F250 Crew
Seats 6 (and 1 is in a car seat).
Removed the behind the seat tank and then also replaced the stock 19gal tank in the rear with a 35gal bronco tank. Added the propane kit so it can run either propane or pump gas and then installed the 120gal (holds 100gal) propane tank in the rear.
With the 3 jerry cans give the atrocious 10mpg rig a 1400+ mile range. Mind you I go broke filling it, but at least I dont have too all that often!
Plan was to add an RTT to the back bed rails and then run a series of valves and t's so I could run all my propane camping supplies off the same tank.
You could build something like this for the price range you described, if you wanted an old hillbilly rig again