Babysitting is a great way, also maybe choirs, or maybe going to the barn and clean stalls like doing the dirty work.
Pick up slack around your barn so you don't have to pay so much for lessons/board. That way you aren't spending so much money and you can save it for other things. I know a few people at my place do chores around the barn for our trainer and they get free lessons & discounts on board :)
Ask the owner of your barn if you can work there for pay, also spend money responsibly and only buy things you need. Good luck!❤️
See if you can work at your barn, muck stalls, feed the horses, or groom horses