For training or for career? If you can only afford $100 and no gym fees then buy some equipment and train at home until you can afford gym fees. Reflex double end bags, small boxing heavy bags can be bought for under $100. Full size muay thai heavy bag can be found for around $100 if you look around. Do home training with that equipment and do all body weight workouts or just pick up heavy stuff around the house over and over again using different muscles. Go online and watch fights, get a subscription to UFC Fight Pass and study the fights and focus on the techniques and fight strategies. Most importantly you have to train, and train a lot regardless if it's at home or at the gym.
Eventually you will have to make your way to the gym to get sparring in until you have the muscle memory and don't need to spar as much to minimize damage.