Effects of having two routers in the same house

I am a complete novice on this subject so please bear with me but what will the consequences be if I pay for my own router to keep in my room? I want to play online on an ethernet-only console but the only router is on the other side of my house and I really dont want to run a long ethernet cord down there. If I buy a second router will that significantly increase the internet bill or something? Can I connect my new router to the one across the house's wifi and be just fine? Any and all information will be appreciated.