How do I make posters of my paintings?

I have paintings that I would like to have posters made of so I can sell the posters. What is the process for doing this? How much does it cost?

ArtWanted does prints from paintings for its members and even sells them for you. I’m not sure if they do poster-sized ones or just how big they go. But you can check it out for yourself.

http://www.artwanted.com/ps/join/