Martha,
I am artist and over the years have probably saved thou$ands by getting frames at garage sales. People often sell picture, frame and all if they don't like the picture - and they sell for next to nothing just to get rid of it. Just ignore the picture in the frame because you can always remove it to put yours in. If I am at a garage sale and see a nice frame, I will buy it for a quarter or two - and never more than a couple of dollars. Sooner or later I'll end up using the frame. Nine out of 10 garage sales you go to will have a nice picture frame for sale somewhere in the pile. If you can wait a few weekends and can do some garage sailing, sooner or later you'll find the right size - that is, if you are willing to have a standard frame size and then find a mat for your non-standard poster size.
Speaking of mats, buying a small cutter and cutting your own mat is cheaper than paying a store to do it. Or you can keep an eye out for mats that are within the frames that you see at garages sales, buy those frames for the mats within, and then paint the mat if its not the right color. Airbrush, if you have access to one, paints mats the best.
Anyway, not often will you find a custom frame at a garage sale because people who have custom frames usually paid for them so they know how expensive custom is OR they have custom for the valuable stuff they wouldn't be selling at their garage sale anyway. If you are looking for more than a few frames that all match each other, your odds go down with garage sales -although it isn't unusual to see two or three matching ones at a time. If it were me, I would go for the metal one in chrome (silver), which is the most common frame and nicest for the money because if you only find one at the garage sales, you can still visit thrift stores for something to match - although you'll pay more there than at a garage sale. Thrift stores always have tons of frames.
If the glass is broken, you can get the frame for even cheaper and then go to a glass shop (cheaper than a hobby store) and buy a piece of regular glass for around $5 (they'll cut it while you wait). Don't pay extra for non-glare glass.
Good luck,
-A.