I'm not familiar with using a Dremel to cut tile, but I can't imagine using any possible Dremel bit to make the kind of cuts you'll need for floor tile.
You can get some pretty cheap tile saws that will work just fine for small jobs.
http://www.harborfreight.com/4-inch-tile-saw-with-wet-tray-3733.html
If you want to go even more cheap, just use an angle grinder with a diamond blade.
http://www.harborfreight.com/4-1-2-half-inch-angle-grinder-95578.html
Depending on the tile you're cutting a tile cutter might work, but in my opinion the cheap ones are maddening to use because they crack as many tiles as they cut correctly, especially porcelain.
You can get some pretty cheap tile saws that will work just fine for small jobs.
http://www.harborfreight.com/4-inch-tile-saw-with-wet-tray-3733.html
If you want to go even more cheap, just use an angle grinder with a diamond blade.
http://www.harborfreight.com/4-1-2-half-inch-angle-grinder-95578.html
Depending on the tile you're cutting a tile cutter might work, but in my opinion the cheap ones are maddening to use because they crack as many tiles as they cut correctly, especially porcelain.