I'd be cautious when choosing a car cover. Less expensive fabrics can lead to scratches on your paint, contrary to what you're trying to accomplish. For a quality car cover that will last a reasonable amount of time and protect your paint from the elements you're going to spend north of $200.
I'm in the same situation (no garage), and I'm looking into a
Noah Car Cover. I've heard good things about them, but I'm still browsing. Best of luck!