Ok, here is the deal with this achievement. Each time you do No Sleep Till Brooklyn on expert vocals you should get $760. This averages out to equal about $10,000 an hour. So thats 100 total hours of that song. BUT, there is an even faster way..this will require you to play though. Sign in the profile you want the money on as a vocalist. Then plug in a guitar or drum set. Go into band quickplay and chose No Sleep Till Brooklyn. Set the mic by anything that makes noise like you normally would and play any difficulty on the other instrument. You should get about $1200-$1400 every time. Reducing the time required by a lot. I guess it just depends on if you actually feel like playing or not. Either way good luck!