Seeing as your Pontiac G6 will be parked outside, you’ll need to make sure the cover you buy is designed specifically for outside use—this will ensure it is both waterproof and can protect against UV rays, pollen, precipitation, etc.
Some car cover manufacturers—such as CarCoversFactory.com—charge a steep price for their Pontiac G6 outdoor covers, ranging close to $170 - $180.
Seal Skin Covers, on the other hand, offers Pontiac G6 covers for as low as $120, and EmpireCovers.com charges a flat $100, so there are cheaper options available.