Hello! I worked at a Hobby Lobby in the framing department not too long ago, and would watch... well, encourage people to spend hundreds of dollars on a top quality framing job, with suede or leather mats and beautiful frames...
The secret is, in Hobby Lobby (I don't know about any place else) they have to order the frames from their own personal manufacturer, they don't make them there. So, when an order is mismeasured, the frame can't be used and they order a new one. This happened all the time. We had frames stacked up in the back room, and my manager would sell them to us for $2 or so a piece. There was one instance where I bought what would have easily added up to a thousand dollars worth of custom frames for $20. Many managers are more than eager to get rid of these mismeasured frames, that they otherwise aren't allowed to dispose of. Also, once you purchase the frame, they will do the rest of the work for a minimal price.
Another tip, Hobby Lobby (once again, don't know about other stores) disposes of matt board after it's been used once. That means, if some lady comes in and wants a 4x6 mat cut, they will make that one mat, then dispose of the rest of the 30x40 board. Our store will either sell you this mat as a "bundle" for $10 (a steal for architecture students and kindergarten teachers) or, you can have a mat cut out of it for the "base price", or the price it would cost you to get a plain paper non acid free mat cut (basically add the length and width of your frame, and multiply by .2, that will be your price) So, as long as you don't mind not having a perfectly even border around every side of the picture, this is totally worth it.
Some framing tips in case this is something you would like to do. Remember that the mat really defines your picture. It's always advised (by me personally) to use the nicest mat that you can. All in my house are either suede (usually with a gold or silver lining mat) or fabric. All are acid free. Second, you don't need to have an exact border on all sides of the picture. I really like mats with "weighting" Take for example, you find an awesome cheap frame that is 15 x 19 ... that's an odd size, but it's beautiful and you think it would go great with your 11 x 14 Van Gogh print, have them put a 2" border on all sides, and a 3" border on the bottom. It looks great. Also, if you don't mind having a 2" border on the sides, and a 2.5" border on the top and bottom, that would look good too. The only thing to keep in mind is this = if your picture is longer than it is tall, the thicker mat should be on the sides, if taller than long, on the top and bottom. Also, don't be afraid to cover parts of the picture. We used to fill some of these miscut frames using these same mats and put in whatever posters we felt like it to sell in the "preframed art" section. We would go wild and use all sorts of fun techniques that we would use on our own art (like floating, ripping, multiple mats with fillits etc...) and we often would only use a portion of a print.
If you have any questions about framing, let me know! Also, if you do plan on buying your frames custom, never pay full price, most places will have half off custom sales!