I used a tent garage for this exact purpose. I picked it up at Sam's Club a few years back, and it was around $240. It was a King Canopy 20X10 model, and the frame was very well made. The cover held up well for about 5 years, and then this year it deteriorated rapidly.
My father-in-law helped me to build a platform out of 3/4" pressure-treated plywood, and we used some 4X4s for extra support in the key jacking points. The cost of the platform was somewhere around $300, but it gave me a level surface to work on our vehicles. In addition, I screwed down the feet of the tent to the platform. It survived heavy winds, heavy snow loads (although I tried to brush snow off when possible), and generally was a very good temporary garage for 5 years.
The only downside is that after 5 years of direct sun, sub-freezing temps, and hot summers, the cover disintegrated this year. The cost of a replacement cover was higher than the cost of a new garage, so you're almost better off buying a new one every 5 years. In my case, we're looking to move soon, so I just took the garage down (and will do the same to the platform during the winter).
I will say that during the winter last year, I saw a ton of collapsed tent garages. I'm not sure what all the issues were, but I saw tubing that was tiny (mine was 2" diameter tubing all around), and I'm guessing they just weren't that well made. In addition, if the feet of the garage aren't anchored into something solid, it's strength is going to be suspect. So, that's a risk that you need to consider when choosing a tent garage.
Overall, for the $550 I had into it, I got 5 years of excellent use out of it.
Another option that I came across was this one: http://www.costco.com/Browse/Product.aspx?Prodid=11523335&whse=BC&Ne=4000000&eCat=BC|50126&N=4047221&Mo=18&No=0&Nr=P_CatalogName:BC&cat=49275&Ns=P_Price|1||P_SignDesc1&lang=en-US&Sp=C&topnav=
I put up a Lifetime 8X10 shed last year and have been very impressed. That model seems like a step between the platform/tent garage I had and one of the shed-type garages available out there like this one (they typically run about $7-8K for a base model):
http://www.thebarnyardstore.com/sheds-and-single-bay-garages/single-bay-garages
Hope that helps!