The only gas class A's currently produced are on a ford f53 chassis.
While these are fine motorhomes, and have gotten better in recent years...
The engine sits between you and the missus, and likes to rev (rendering conversation difficult)
and the chassis is on leaf springs, not air bags.
Cost, IMHO, is a non issue. For every person who says a gasser is cheaper to run because gas costs a few cents a gallon less, there will be 6 who say a diesel is cheaper to run cause they get better mileage (even though they cost 4 times more to buy in the first place) :)
The "big thing" these days is smaller DP's, there are a number of 32-36 foot diesel pushers being produced today that could be very nice.