This is the cheapest project I've made so far. I found this glass medium pebbles at Michaels Store on their flower decorations section for only .89 cents and use nice pictures from magazine and left over from my scrapbook making.
Puncher if you want different kind of shapes
1. Put some Mod Podge behin the glass and attach the paper.
2. Attach the paper and cut-out the excess.
3. Apply some more Mod Podge at the back of the paper and the magnets.