I haven't driven a Promaster but from what I've seen and heard on job sites is there is a good reason why they are cheaper. The difference in build quality between them and the Sprinter or Transit is stark. That said a AWD Transit will be significantly more expensive and I don't believe it's available with a diesel. A Sprinter with 4wd($8000 option) is likely out of your range.I have an interest in my household for a camper van. The Promaster seems more in my budget. I'm also thinking about getting just the van and making the inside livable myself.
I suspect FWD would be a must vs RWD. I don't see any 4WD, yet.
The biggest question is Diesel vs Gasoline. What is preferred for camping/traveling anywhere in the US?