Shop around for the best price and be a little open as to the size. Sometimes you can get a good deal on a cancelled order that is a little different then what you want and save 30% or so.
I am in the market for a 30x90 or 40x70/80 myself... I sugget you go with a 14' tall building and get atleast one 12'x12' door.... for resale value - people could fit an RV in that way.
Don't forget to include insulation, door openings, doors, foundation, engineered designs (for your building permit), sky lights, vents, and painted sides (not just plain galvalume) in your final costs.
There are a million places to get these from - many seem to be from Texas.
Good luck