Larson Carter

I'm at a total and complete loss on what I should do. I'm only wanting to install 1 12" or 15" subwoofer under my driver side rear seat. I don't know much, but I'd only like to get around 800 watts. So nothing too crazy. I would like to have someone help me find everything I need. I want to keep it around $500, and refub and used are okay. Thanks for all help.