Harbor freight aluminum oxide. I use it in my blast cabinet. It's going to be your cheapest route. I have tried every kind of media and it is the best general purpose. Also note I use this for industrial work.
I would recommend walnut then. You need to stay away from glass or aluminum. They are bad for breathing. Unfortunately harbor freight is still your best bet for price locally. Some welding supply stores carried it in the past, but I don't believe they do anymore.
Hey BCS, I've been told soda ash can be used to blast things like hard plastic resins or hard woods since it's less abrasive. True? Not true? I have some Pelican cases that have a residue inside them that I have not found a cleaner that will remove. Soda ash blast has been revommended but I haven't found anyone that knows anything about it. Any suggestions?
I use walnut on wood blasting. Soda ash would require a special tank, or an adaptor. I buy mine at harbor freight as well. They are just easier for me to get to and cheaper.