Besides Home Depot or Lowes, be sure to check your newspaper want-ads and you might even try eBay.

Some of the metal ones at Lowes is fairly reasonable...

I bought a canvas carport at Costco for less than $200 and I use it in my backyard for storage. It holds up against the windstorms and doesn't collapse under a 4 foot snowload that has partially turned to ice, so far. I put old panelling down on the ground and this is keeping everything quite well out of the weather.

I had one of those metal sheds, that is made of all those sheets of corregated metal, and this tent is much easier to put up and take down than that one was.

Go to a local moving & storage company, get two 190 cubic foot ( overseas ) shipping containers set them up side by side, get them level, join the two units together using, bolts, cut out the inside walls with a circular saw, buy four to five sheets of corrugated steel panel, for the roof, completely caulk all top and, side seams and, seal the roof with Kool seal. this will give You an eight by eight storage building. the only other thing You will need to buy are hinges and, handles for the doors. moving companies usually give away the crates at no cost.