I have about 50 "support rings" that hold eggcrate (plastic grid) above the drain water in plant trays, which lets you fill the tray with more water and helps keep the eggcrate clean. Never used  free for actual shipping cost (probably about $7.50).

These are basically uniform 1 5/8" (41 mm) high slices of 1 7/8" (48 mm) diameter PVC pipe. They are very sturdy.