I found these tiles at Lowe's for cheap.. I'm talking like under $3 per sheet (I originally bought two, but ended up needing 3..so it will still an update that cost less than $10).
All that I did was pull of each tile, attach a little hot glue to the back and then place it on the mirror. I had to put it over some clips as they would not have been thick enough to fit between. I also had a problem at the bottom of the mirror. I had a space that was less than an inch left on both corners and ended up having to go up to Home Depot and beg for them to cut my tiles. Nice guys! : ) But on that note I would recommend measuring before you start gluing.
Here is the finished product, a quick and easy update!