Bill's right, there are some issues to deal with on a fiberglass body. My last CJ had a FG Tub, but the problems I had were minor. A lot has to do with the manufacturer. Beware of the "cheaper" manufacturers. Mine was a 4WD Hardware Body, Quadratec's are also good quality, maybe even better. VERY Solid, though, reinforced with wood and steel core in the critical areas.
My next project will have either a Fiberglass Body again or possibly an Aluminum Body! I can't use steel, I live in the Northeast, salt capital of the world, steel is not even an option.
Aluminum Bodies are the new thing, but cost on the order of about $2600 for just the tub (although worth it, a budget issue).
A good Fiberglass Tub will be about $1200 to $2400 depending on the grade you want and whether it is Fiberglass or Kevlar. Quadtratec offers the tubs in 3 grades of Glass, 4WD Hardware offers one good solid tub.
Personally, I would go with Aluminum (now offered by Quadratec), if funds allow it.