How do I sell a poster design?

I had a great idea for a poster recently which I have now designed. However, I'm not sure what to do next. I thought I would be able to get a printing company to print the design for me and I would sell the posters on eBay, but it turns out that the price to print them range from about �12 upwards! So what can I do? Are there any companies that buy poster designs off of you?