I think I've found the quickest, easiest way to get this Achievement. Having just unlocked it myself, I can say that I managed to get 500k in a week with this set.
Right, so you want to be playing Expert Bass on your profile, and have a second profile/player on Beginner Vocals at all times.
Play the following;
Dammit - $1,235 - 2:41
The Kill - $1,380 - 4:11
The Middle - $1,195 - 2:50
Rebel Yell - $1,860 - 4:47
Scream Aim Fire - $1,610 - 4:27
Stillborn - $1,105 - 3:11
So that's roughly 21 minutes, and around $8000.
This adds up really quickly.
Another way is to just play Dammit over and over again as it's really short and gives you over $1000 a time.
It will get very boring though, but like I said I got half of the money in a week, playing for about 5-8 hours a day.
Good luck people and have fun, even though playing this set for the next 50 hours will get very boring. =P
It may be wise to put in some of your favourite songs (Unless these are your favourites, in which case, you're set!) from time to time so the setlist isn't as boring.