In pickups, I would go further back, look for F-250 or E-250/350 with the 460 V8 or C2500/S2500 with 454 V8. That would be G2500/3500 for the GM van, or you might find early Express/Savannah with Vortec 7400 or 8100.
Although the older big gas engines do not have the high peak HP ratings at high RPM enjoyed by smallblock V8s now used, they have much better torque at the lower RPM you will use for cruise.
These gas pickups and van tend to drop into the $5000 to $8000 range here at 10-12 years old, the trick being to find one under 150,000 miles.
Actually, your budget would buy you a newer E350 or F250 with the 6.8 V10, where the market is now for 1999-2004 model years, it is just that they are hard to find because they were usually ordered to do a specific job (usually towing) and don't get sold until worn out.