I agree with Jim Fogle on Fiverr as well as what Joanne does. There is probably more money to be made helping other musicians by selling your services to them. Akin to the Gold Rush - The people that made the most money were those who sold equipment/services to the miners. There are also services on Fiverr that promote music. Not sure how successful they are.
I make about two to three thousand dollars a year on Fiverr and that is with little promotion on my part. Not a fortune, but it provides enough for equipment/software upgrades and more.