I would definately recommend a basement over a crawl any day. The real cost differential between a crawl and a basement here in Michigan is around 6-7k, last time I checked, but it's been awhile. Definately shop this around. I don't think the cost to set up the house would be any different whether it's a crawl space or a basement.
Your basement will offer lots of premium storage space for stuff that I personally would not want to clutter up a garage with. I would have gladly paid an extra 6k to have a basement under our house, but it was an existing house, plus it's on water, so a basement is out of the question anyway.
We had a manufactured home set up on a lot about 10 years ago. It was brand new at the time. We only lived there about 2 years. We had a very hard time selling it because it didn't have a basement or a garage. Obviously a garage is easy enough to put up, but not the case if you don't have a basement.
Also, if you're in such a position that you can actually choose between a manufactured or a modular, I would wholeheartedly recommend a modular over a manufactured. We love our manufactured home, but financing is a royal PITA. Most mortgage companies want nothing to do with manufactured housing, even if it's on a private lot. Sure you can get them financed, but you will severly limit your future buyers if you should choose to sell at some point. I'm refinancing mine now, and am having a difficult time finding any mortgage company that will allow me to unlock my equity, and give me a good rate. Seems like there's always a penalty because it's a manufactured home.
By the same token, if this house were NOT a manufactured home, we wouldn't have been able to afford it, since it's on water.
If you DO decide to go with a crawl rather than a basement, I would highly advise you to go at least 4 blocks, but preferably 5 if possible. My house is on a 3 block high foundation, and it's miserable to access it because of the steel frame that hangs down. It does have a poured floor, and I use a mechanic's creeper to get around under there. Still too tight though.