It's fun taking something apart and putting it back together again in a new creative way. I work in an office where we had a lot of old promotional type posters that were very expensively matted and framed. Now that we're moving to a new office we wanted something new, but didn't want to spend a lot of money decorating. We decided to disassemble the old frames and re-use the mats to frame new prints.
We made a visit to a local craft store and found an abundance of inexpensive artwork in all sizes, ranging in price from $1.49 to $40.00. Definitely within our budget. We picked out several beautiful floral prints and framed them with the old mats and frames. Disassembling the old prints included tearing off most of the prints that had previously been glued to the mats, but I just tore it all off and used scotch tape to tack down the new prints.
The new prints don't have to completely fit your frames or mats, either. It was hard finding prints that were just the right size. Don't be afraid to move the print around in a mat that's a little too small. Often you can cover some edges of the print and not take away from the overall effect of the picture at all. Just trim edges where necessary to make the print fit (after you've double checked your positioning within the mat). You can also buy bigger mats to make a smaller print fit in a larger frame.