well, more specifically;
a fairly well known underground metal band, has around a $500 to $1000 paycheck from live shows, but sometimes it's $0 too.
Bands that you have in your record collection make $1000 to $5000 depending on numerous things, local market factors being the most important. For instance, they will get paid more anywhere in Europe than say in the United States.
Arena bands like Maiden and Metallica make six figures from concerts pretty regularly.
Sharon Osbourne is quoted as giving Maiden $180k per night on Ozzfest, which is likely accurate.
Van Halen was paid $1 million from the 1983 US Festival in Los Angeles, CA, which I believe remains the world record.
A promoter in Los Angeles told me he paid has-been metal bands around $1000 to $1500 to play in various clubs.
For better or worse, there is no way to determine a particular band's income without seeing their books.
As far as musicians holding down jobs, I would think that in metal, all the bands from the United States, save the big ones like Slipknot and Metallica, have day jobs to support themselves/families.