man i hate sheetrock. If i was trying to save money, i might hang it myself, and have someone else finish it, especially if you don't have much experience with it.
Also, are you going sheetrock on the ceiling? Thats a huge pain.
Anyway, if your going to have it done, pm me and i'll give you the names of the sheetrockers that i've used in the past, whether you use them or not, at least you'll have another couple of quotes....
Vinyl Siding - i've only used it once, and i had it done. I know a guy that does that as well...
I really don't think its all that hard to do, but if your doing it all the way and covering eaves, you might need a break to do it properly, and i doubt they're cheap. Might be able to rent one, i really don't know.
Edit - my parents built a cabin several years ago, and they did the inside in unfinished paneling, and finished it themselves. They used acoustic tiles for the ceiling and it came out looking great, was much easier than sheetrock, and took less time i think.