What?! You've never seen them? Well let me tell you, it's easy and cheap! Just visit the engineering prints page at staples.com to get started! The website says that engineering prints are not suitable for photographs, but if you have a good enough camera (ours is 10 megapixels), it works just fine!
Your size choices are 18x24, 24x36, and 36x48. Of course, the $2 poster frame I thrifted was none of those three sizes.
(That thing rolled up on the frame is the print. They print out your photograph on very thin paper).
Most photograph editing programs have the capabilities to crop the photo to the right dimensions. After cropping the photo the way you want it, upload it to the staples website, select what size you want, and it will be ready to pick up at your local staples before you can say "Decorating on the Cheap is more fun than watching Magic Mike!"
When I made mine this morning, it cost me under $3 plus tax to make a 24x36 print. I'm not sure if that was a special sale or that's their every day price, but other bloggers have quoted slightly higher prices.
When I picked it up, for some reason it was still a little larger than my 22x28 frame. I just had a little extra trimming to do, and then it fit into the frame perfectly. I <3 how it turned out!!