I'm seeing around $20k for used vans with 1-2 years, 20,000-50,000 miles, $10k for 6-8 years, over 100,000 miles. Usable brand name B's in thes age ranges may be 2-3X the cost of a a bare van, but a home-built camping conversion seems to carry only a small price premium, just like basic fitting for other jjobs, HVAC or sewer cleaning equipment.
Beyond that age and mileage range, the market is pretty much off AutoTrader where I look. To get down to $5000 and be usable, you are probably going to have to go out to 20-30 years old, hope for something less than 200,000 miles. People don't usually stay with a van this long and trade, once past 8-10 years it is more like keep it and use it until it no longer runs, or the owner dies and the heirs don't want it.
Brand probably doesn't matter much, you'll want just about anything that has the equipment you need, in working order. A lot more companies tha today were building conversions, including camping, 30 years ago, but fitting weren't as luxurious. One or two seats that will become a bed, a cooking surface, icebox or very small gas fridge for cold storage. Screened windows for ventilation, air conditioning became common more recently as buyers were willing to pay a lot more. Pop tops or raised tops weren't universal, many camped bent over with heads ducked, pop up tops were usually to provide an upstairs sleeping place.
I'd be looking for an old Westfalia (VW only) or Sportmobile conversion, but price is still likely to be a problem, since VWs particularly have become collectible and prices are way out of line with function.
In the age range to get you your price, 1970s to 1980s, Coachmen, Coachhouse, Shasta I think, were in the conversion business, Dodge vans earliier, Chevy and Ford later. Also many smaller companies that went out of business during a sucession of fuel price crises and market downturns.
Do you think you might want to find a bare van at that price, and install camping equipment yourself? There are a lot more old work vans out there at your price, and they'll be more recent, though maybe also much higher mileage than a seldom used camping conversion.
Nationwide search just found
97 Jayco 19 at $8700
84 Fiesta on. Ford , $6000
88 Falcon on Ford, $6500
all about 100k to 150K miles
If you can bump your budget to $10,000, you can find a lot more in the mid 1990s, around 150,000 miles more or less.
