We use the Car Jackets on many of our cars...but, they are for INDOOR USE ONLY!
A breathable car cover is the only real option for outside...another choice might be a small "free-standing" canopy style tent...you can also get enclosures for these. The total cost will be a little more than your budget...but, when you are done with the car storage you still have the canopy...worth considering. You will still need an inexpensive breathable car cover...but, the tent will do most of the work.
http://www.shelterlogic.com/ProductL...anopy%20Series
http://www.shelterlogic.com/ProductDetai...Canopy%20Series