I do a lot of outside container gardening at my place since my soil is so bad. You would be surprised at the things you can use in the bottom of pots to aid in drainage. I never use perlite because it comes out the drainage holes. Save all those little mesh type bags that things like potatoes and onions come in, sometimes I get cherry tomatoes in a smaller bags. They use these type bags for a variety of products, not just veggies. I like to use things that have very little weight to them for my drainage layer. I fill these bags with things like empty medicine bottles tightly capped or styrofoam peanuts--makes for a great drainage layer.