The most important thing at that vintage and price-point is what actual condition its in right now. Has it been cared for and maintained over the years? Or, just left in someone's back yard.
Looking for water damage, rust and ensuring general maintenance upkeep on all vital components (engine, chassis, generator, etc.) will be more important that the amenities inside. You can always change those to your liking and budget.
I'd also keep some money aside for repairs (both to get you initially road-worthy, as well as for the inevitable needs further down the line).
Floorplans of that vintage don't vary too widely; there are pretty much only a handful as you'll see as you start looking around. Definitely make overall condition your first priority, then everything else behind it.
Best of luck to you in your search!