What are you doing with the car? Why do you think you need more aggressive brakes?
If you want a good performance upgrade for
really cheap, find the most aggressive front track pads you can. They will eat through the front rotors quickly- but from Bimmerworld the ti front rotors are $20. So treat them as disposable- buy a half dozen and replace them as you wear them out.
It's dirt cheap, it will give you a very nice brake improvement, it could not be easier to install, and it adds not an ounce of unsprung weight. Everything else will add weight where you don't want it (trust me, M3 front brakes are
much heavier). If you're autocrossing or occasionally tracking, it would be hard to find a better option. Granted it won't stroke your ego like M3 brakes or Brembo rotors- but you get to decide what's most important
