Might need something a bit more heavy duty....
My car tends to sit on the drive under the cover most of the time!
It all depends on how serious and how much you want to cough up.
I have car cover for my 106 rallye show car, that was well over £350.
The problem you have is that cheaper covers will probably do more damage to your car, because of the material used for example:
Mine is tailer made to fit the car, if the cover is loose then it will bascially act as sandpaper on the car's paintwork in windy conditions, this again is from the material used and poor fitting of the cover.
Also if the material isnt breathable then what happen's, is that a microclimate forms between the paintwork and cover causing the paintwork to fade. This is when moisture cant escape.
Also covers protect from UV rays which dull interior and paintwork.
However you cant beat getting it in a garage,I only had my car out for one winter but the cover was well worth it.
I got my cover from "Covercraft" you can find them in the back of Evo.