Okay it sounds like you aren't a very rich person (if you'll forgive me bringing up the crass subject of finances) and neither am I. What i do is work with what i have and if i find that i'm regularly finding my gear falling short then i will then look at something that will cover the problem i have. If i can't afford it i read up/experiment with my technique.
So over time i am better in those situations anyway and then i re-asses, do i still need that bit of kit?
Okay so you want shots of cage fights, i've never been to one but i'm guessing you can be a bit away from the ring and it could be a bit dark?
Look at the shots you've taken, are you having to push up the iso? is your shutter speed getting a bit too low to catch the action? to hold the camera steady? Invest in a faster lens (wider aperture/lower f number) or learn to expose properly and how to hold the cam steady and time your shots better.
Are you a bit far from the action? Invest in a longer lens (more mm) or figure out how to get yourself closer
Some of these options will cost you a lot more than £200, some are free... go for the free ones first