I remember vaguely in interview with the Black Keys talking about selling out or whatever, anyways they mentioned how they turned down £200,000 so their song wouldn't be used in a mayo commercial even though they had no money at the time. I'm sure Gaslight made a nice chunk when Casanova Baby was used by USPS since it was a deal through S1D and not Mercury. Also they probably do really well with merch sales since it seems like they constantly release new shirts/posters.
Relatively speaking, Coachella is probably the largest festival that they played this year.
"There are only so many big-name acts to anchor a big festival, and they earn good money. While the lowest-rung act at Coachella made $15,000 in 2010, headliners can command seven figures. It's turned into a nice living for some acts."
Honestly, If i were to guess I'd guess that Brian and them make comfortable 6 figure salaries. I'd ball park they make probably 25-50k/show which is a pretty conservative estimate. Also keep in mind that they have to pay a bunch of costs associated with the shows as well and there are probably other people who get a percentage of it as well.