I shop at thrift stores for framed art. Frequently it has mats. I take the art out, touch up the frame and rarely pay more than $10. The hard part can be finding the perfect frame for a particular photo. But I have found that sometimes it is a surprise how photos and frames will go together. I keep a supply in my garage, especially simple/plain frames.
I do exactly the same. Our thrift store has an unlimited supply of unwanted art work. I also have 10-15 frames waiting for my images.