Try shelterkit. They have do it yourself kits that might come close to your budget and needs. A friend built a house out of one of their barn kits. Yoouch! I just went online to look at their links, outragious how high their prices have gone. www.shelter-kit.com/
I built a garden shed from recycled materials for about 120.00 (4x8 feet)this year. If you buy 2x6 for framing, use something like t-111(cheap siding) and pour your own cement slab, you might come close to 3000.00 for materials! The size you want is going to cost alot in the end, plus permits because it's greater than 8x10 feet. Might be cheaper to rent a storage unit like Don does for his project 3k build. After Katrina hit, and the gulf war, the cost for basic building materials has skyrocketed. Do you live in snow country. If so you might need a beefier building to support the weight of snow on the roof. Some of the smaller steel garage buildings/ shed/ shops might be the cheapest. What ever you build, think whether you want insulation to keep warm in the winter months! Good luck and keep us posted! Steve.