Ford's specs on the current F-250 XLT SRW SuperCab (I'm going with the SuperCab to split the difference between regular and crew, we're just ballparking here): about 7000 lbs curb weight. Obviously your real world results are likely different but it gets us in the zip code.
Frontal area:
http://ecomodder.com/forum/showthrea...ement-462.html
I saw someone else's estimate of 38 sq. feet for the F-250, that sounds close.
20mpg moving a bus that size down the road is, frankly, pretty good.