With that low budget, I suggest that you look to used DH brakes because that kind of money can only buy new crap.
Off season, you can find a good brake set for 150$ on Pinkbike, for DH racing fashion makes many riders change their brakes quite often. Nevertheless, best brakes are expansive and even a used set is more in the range of 200-300$ when you include mounting adapters and new pads. If you are building performance, that is the minimal investment IMO.