Salary
Average Salary: $65,000
Expected Lifetime Earnings: $2,713,620
If you're talented, persistent, get along with others, take direction well, and can play anything put in front of you like you're possessed, you could make some serious money. Like 100,000 a year serious (source).
More realistically though, your pay will average around $60,000 a year (source).
If you join a union, you'll have to pay dues and set aside part of your earnings for your pension—however, you get to earn union minimum, get health insurance, and get the legal back-up in case somebody tries to stiff you. In other words, you'll have a safety net—always a good idea when you're a contract worker.
Union rules say a leader or studio contractor makes almost $800 for three hours of time or fifteen minutes of recorded time, while a union side musician makes half that for the same amount of time. For three and a half hours, it's a thousand dollars, or a little over $500 for a side union musician. Bump that up to five hours of time and the fee goes up to over $1800 for a lead and $900 for a side union musician—plus overtime and all sorts of extras. This isn't exactly chump change (source).
If you're just starting out and are looking at non-union gigs, it's only $40-$60 an hour (source); however, that still beats the pants off minimum wage.
Of course, your talent and experience level will dictate your salary. If you've been jamming with Bono and the gang for a while, you're going to command top dollar.
Depending on where you live, you could get a steady stream of work. Urban areas like New York and L.A. have a lot of studios to work at, as well as industries like film, TV, live theater, awards shows, and commercials that need musicians to step in. Again, working union gigs will keep your salary high.
You're probably also going to need an agent if you're working at a high level of union work. And don't forget you'll have to pay them 10%-20% percent of your cut (source).