As Steve B said, 'keystone badge' still leaves a lot unknown. The drum is probably worth no less than $150, unless its in poorer shape than stated. If its a 1980's-2000 keystone badge model with pitting, then that's about what its worth. Its probably no newer than 2000 if its pitted, so its probably not a real recent keystone badge model. If its a 1960's keystone in good shape, its probably worth $250 +/-. If it would happen to have a chrome over brass shell, it could be worth more, but I don't think it would be pitted with a brass shell.
Just remember this: there are always tons of these for sale. Don't feel like this is the one you have to buy. If you look at it, and are not sure, then pass. There's another one to buy. I have bought and sold a few of these over the years. I bought one a couple of years ago on CL for $100. It was a 1980's keystone that the guy used for teaching. He's now running a pizza shop and just wanted to get rid of it. It has zero pitting. It just needed some clean-up. I also changed the heads, snare and strainer (my preferences) and I have really nice Supra.