I paid $750 for my 1973 high top Dodge camper van that had been stripped by the previous owner, then spent $200-$300 on re-inventing the interior. That was 11 years and 250k+ miles ago. It had 200k miles on it when I bought it, and it now has over 450k miles on it and other than normal maintenance it has been 100% reliable, comfortable, and trouble free.
It has pre-computerized 3188 engine with a 727 automatic transmission. It gets 15-16 mpg in town, and a solid 18 mpg on the highway.
I did a low tech/no tech but full featured and self contained conversion including a toilet & shower, kitchen, comfy futon sofa/bed, swivel recliner, and of course heating, cooling, and power. I’ve lived comfortably through winters as cold as -60°F and both very hot & dry and hot & humid summers. Swamp coolers work great for cooling, you want the indirect type, and they also use very little power. For heating and cooking I use wick type kerosene (multi-fuel) appliances. No propane on board.
I’ve lived in many vehicles since I started in 1973, and with a single exception never paid more than $2500 for any of them. Normally buying an old motorhome is cheaper than converting a van, and move in ready.
Forget the expensive stuff like insulation, solar panels, roof vents, and 12v compressor fridges. An under $20 fan in an open window gives much better ventilation than a $250+ roof vent. Shade works better than any amount of insulation, and the necessary ventilation defeats any insulation any way. I get nearly new deep cycle batteries from junk yards for under $20 each, and they usually last 5-7 years. I charge them while driving, or with a $99 generator combined with a $29 battery charger on the rare occasion that just driving isn’t enough. I use a cheap ice chest with 99¢ big blocks of ice that typically last over a week, no more broken expensive fridges for me.
Vehicles from the 70’s and 80’s are both cheap and reliable. I’ve had the best luck with Dodge’s.
Holler if you need more…
"Be the reason someone smiles today!" ~ Van_Dweller