Hey I DJ part time; It honestly depends on what kind of Music you DJ and the scene you're in. Most DJs support their career as well as fuel it by producing as well. Gigs can pay anywhere from £50 all they way up to £5000 depending on fame and experience.
Learning to produce and getting signed to a label is honestly the best way to achieve this as it gets your name in the scene and ultimately lead to more bookings. Treat it as a side hobby but also get involved in the scene. Get to know other producers/djs as well as promoters as ultimately these will be the people who you will work with as well as get you paid.
During my time at University I produced on the side and managed to get signed to an independent label where my First ever vinyl record got released on - After then I was booked to play at many large venues and parties in London as well as get to play at a festival in Valencia. I'd make sure to collab with other producers to help build each others brand. However, this was never to be my main source of income, and was (and still is) a fun hobbie I'd do on the side outside my normal work. - Protip: Learn how to mix on Vinyl as its more unique than CDJs or Laptops and tends to get noticed more
There is no simple formula just keep trying and it will slowly come together. Most importantly have fun!
Feel free to ask any more questions you have about DJ'ing or production.