If they both are running the same engine, a V-10 say, I would not expect any real difference in cost.
You may want to be specific on what models you are considering.
I think you need to specify what size you are talking about. A 40 plus ft Diesel Class A with all the bells and whistles or a small Trek with a 454 V8. Just as a triple axle 5er cost more for axle service than a double axle and a Diesel engine cost more to service than a gas engine.
I believe a CLass A generally requires facility set up to handle large vehicles while the pick-up does not. However, for the DIY inclined I suspect you can change the oil, filters, etc on either in a convenient driveway if you are so inclined.