Amazon has Bloem Ups-A-Daisy Round Planter Insert for $7.98 (Reg. $17) with free shipping on orders over $25 or with Amazon Prime orders.
Ups A Daisy plant elevation platforms are specially designed to help reduce the amount of potting soil required to fill large pots. Insert sets inside your planter approximately halfway to 2/3 of the way down into your container. The insert elevates your flowers and plants out of potential excess water that gathers at the base of planters. This is a great solution for preventing root rot and mold issues and allows for essential oxygen to access plant roots.