Sears just recently had the metal ones on sale... they may still be on sale, I'm not sure. I've been thinking about getting one. I can't believe that they're actually that hard to put together... but remember to factor in the cost of a floor, regardless of which kind you purchase. They rarely come with floors (or include floors in the cost of the kit or prefab ones). IMHO, I would prefer a metal one, as I don't want critters chewing through the walls to get inside, or insects deciding that my shed is yummy. Try looking for plans to build a custom metal shed... The materials can be purchased at Home Depot just as easily as for wood sheds... and it'd be less expensive.
edit: incidentally, my workplace just built a huge storage shed/garage against the rear of the building... It was built quite cheaply, but looks really good and is sturdy. Wooden frame covered with the corrugated metal panels. I'm trying to remember offhand, but I don't think you even need 2x4's every 16 inches as you would with an all wood structure. (except on the roof... heavy snow loads expected, but even there, I think they're spaced 24 inches)