Go to a local tile store and get a few unglazed quarry tiles for about 50 cents each, my $30 pizza stone hasn't been used in 3 years. If a tile cracks big deal leave it there or if you want to replace it it's only 50 or so cents. Measure your oven rack then go buy enough tiles easly fit cover the rack, for me it took 9 tiles, $4.50. I place the rack in the lowest setting, add the tiles and leave them there. The oven will heat more evenly when baking cakes, bread, roasts, etc. I even bought a third rack to use when in those rare cases I need two racks.