My favorite. Last about two years in the wild. I used a size #3 for my Prius v, but I believe a Size 1 is the one for the c. Budge Lite Car Cover, Basic Indoor Protection for Cars, Size 1 - Walmart.com
I just purchased the cheapest one I could find on amazon, and tie it tightly around the rims so the wind won't get in: Its a big for the prius C, but also works with my GF's hyundai accent., the strap material is fraying, but I got mine for $21.73 so i don't mind.