You might find a true class B in that price range, but but I'd expect it be pretty well used up.
Yes, hightops are almost always f'glass. You should have no trouble gluing solar to it with the proper glue and prep. # of batteries depends on the quality of the conversion and previous owner's needs. 11OV connections will depend on the installation of outlets inside. I got as high as 15 mpg out of my '01/'02 Chevy Roadtrek 190 with the 5.7, usually more like 13-14. I'd expect a lighter van on a 250/2500 to do 1-2 better. Fords have tight cabs, and some have handling/tracking issues. Some Chevy van owners complain about easily-overheated brakes; dunno if this is the driving style or an actual weakness.
A quirk of later Dodges (limited to '98 and on, I think), at least the one I owned ('99/'00 RT 190 on a 3500) and many others that I've read about... scary squirrely handling, particularly around semis. I tried to cure it, couldn't, and sold it and got the Chevy solely for that reason. But I'd _have_ to take any van for a test drive in person, especially a high-top Dodge or Ford.
Jim, "I've reached the age were 'Happy Hour' is a nap."