OH MPG, in that case, ITS A BUS who cares about mpg. Lets look at the numbers, NY, NY to LA, CA its about 2800 miles. Assuming $3/gallon
@10mpg its 280G of diesel= $840 good modern bus
@9mpg its 311G of diesel = $933 Average bus/ modern Detroit diesel
@8mpg its 350G of diesel= $1050 Vintage bus
@7mpg its 400G of diesel= $1200 Vintage Detroit Diesel
@6mpg its 466G of diesel=$1400 bus with problems
plane ticket one way is about is $225
car with 30 highway mpg $3/G would be 93G of gas and $280
It would also be 46.5 hours on driving time @60mph
Yes it would be expensive to drive from ny to la. How many times would you really do that?
If you are concerned about MPG while seeing the country I would suggest something like a prius or nice TDI vw (better performance and mileage but worse for environment). Tire pressure, Tire condition, road condition, and loads will all change all of these things. I doubt most road trips are this long round trip. If you are not taking a tow vehicle you probably won't still drive your bus to get dinner or to the grocery store (unless it is en route). Think of driving a bus conversion in part as driving a home/hotel room on wheels not just a vehicle.