Look around for a rolled or slightly burned F250 & F350. I bought a rolled F350 crew cab for $2,200 took the axles, transfer case, tranny and all the misc parts off of it. I was able to get the motor running. I sold that and a few other parts and actually made money.
You have to look closely, a bent frame kills the deal for many that want a chassis. For a van you don't care. Stay away from severe front end damage.