Hey Roberto, for $3, you might try a Mr. Clean magic eraser for minor scuffs and cosmetic wear if you are looking to resell your phone. Take a look on google for some how-to's and instructions.

iFixit is a Do-it-yourself community of people who share how to repair devices, however iFixit doesn't offer any repair services. If you need a quote to restore it to like-new condition, you'd have to take it to your local phone/computer repair shop.