I vote for Costco, if you have one near you.
My printer prints 13x19, but for the actual cost of ink and paper Costco is a better deal and ready in 1 hour if you're not getting the "Poster Size" of 16x20 or 20x30, those 2 need to be mailed to you.
11x14 and 12x18 are $2.99 each, very cheap.
Remember though, depending on the camera's imaging ability (megapixels), your image may not look so good blown up. My old camera was only 6 Megapixels and at 13x19 it was really pushing the camera's resolution. This is an issue of perception though, at 4 feet away and farther it looked fine, but close up you could see the loss of details.
Costco's site will warn you about going too big on a print after you upload a file, incase you don't know yourself.
Cheers.