Find a sandblasting type supply place in the yellow pages. They'll sell a 50 pound bag of corncob grit for about 20 bucks. Could be a lifetime supply for some. I go through a bag or so a year.
You can add your own polish to it, or just run as is. Both clean. Only one shines. I could care less what my brass looks like as long as its clean and works. But I have shot upwwards of 20K rounds a year and can't waste time on cosmetics either.
Dillon and midway both sell liquid poishes to add to your cheap cob. I used walnut one time It got some nasty residue all over my cases that wouldn't come off... its not cheap. I see no use for it.
Generally the conrcob media cleans well but doesn't give the high jewelry bright finish that the walnut hulls impregnated with jewelers roughe does. Kind of a so what thing except that the higher polish may make resizing easier though I have never noticed a difference.
One guy I work with swears the rouge packs into the inside of the cases and has to be picked out. Again I have never seen that but never say never.