Start by looking at the threads that have been started recently on purchasing vans. A lot has been covered on what to look for. Mostly rust, but some have known defects that make people run away from them.
Whatever you buy, estimate another $1,500 for repairs that have been put aside. A transmission will cost, the motor, The rest of the things are $$$ also.
I have a $500 van, that has eaten another $1,000 , but only because I did most of the mechanical work myself. It still needs another $1,200 in solar, and the AC. $150 to $500, a steering box. $100 because I can put it in myself. (Otherwise $200.) The motor and transmission was good, so this was worth the money invested.
It is a 1991 Dodge Ram250.