I think you compare high prices of Sprinter-based class B.
Mercedes is not going to be cheap, but even I don't believe in 20mpg some owners report, my MB diesel sedan does make 35 mpg.
I had similar situation with our conversion when city made ordinance that prohibit parking it on my 1/2 acre.
Going to the storage was annoying and when sons moved out, I bought Truck Camper.
Having truck already it was no brainer and slides make TC very nice RV.
Did I mention that TC has no annual fees and you don't have to worry about tires that age before wear?