We're talking about saving a couple dollars here, why not just buy the media from the gun store?
Maybe I'm not changing my media often enough but I really see no reason to try to save a dollar or two on my tumbling media. I run the same stuff for close to a year, run thousands of pieces of brass through it and just throw an old dryer sheet into it once in a while to grab some of the crud out of it. My brass still comes out shiny and clean. I probably spend $10 a year on media. I can think of a lot better places to try to save money.
I do think I'll give one of the bags of Walnut at Princess Auto a try next though, I'll have a lifetime supply, will actually be more of a pain in the arse to store the bag than the money savings is worth.