Hi & to the forum. Average mpg will vary between 19 - 30 depending on your drive & how heavy your right foot is. If you buy parts from the Nissan stealers then they can be expensive, best to stick to the traders on the forum. Check out the buying guide in the intro section. Usual things to check for are the clicking axle, skipping Bose & intermittent left speaker. Good luck with the purchase & if you have a link to the car then post it up and we can give our opinions.