I understand that money can be tight on a bands budget, but can you and your band sleep in your van rig? Is your 10mpg pulling a trailer? If your not sleeping in your van, you have to factor in sleeping expense into your total budget. Also, with a bus like the one from ebay, its large enough to fit a kitchen area with a small range and fridge, which means you can cut a little more off your travel expense with food you can bring.
I would imagine this rig may even have a cummins 5.9 in it. I'm not familiar with all the models of bus that was an option, or which chassis manufacturer used it, in which case you could probably squeeze 15mpgs out of, perhaps? I would imagine even if the bus had the 6.9/7.3 its more then 8mpg..I think maybe 11 or 12..anywaay...just more thoughts =^)
1985 22' Wayne/lifeguard body, IHC chassis, 345ci, 4 speed
1985 Ford Ranger 4x4, 2.3l I-4 turbo diesel, 5 speed
1975 Mercedes 240D, I-4 non turbo diesel, 4 speed
1995 Volvo 850 Turbo, I-5