The cheapest tweak is to take care of your ears. After 40 years of being a professional musician, my ears are in decent shape. I can hear in a reasonably flat fashion, but I have tinnitus that makes it impossible to listen at the levels I would really love to hear. Above 70db A weighted, it starts to get uncomfortable and the ringing ramps up. Take care of your ears, people. Unlike all the other tweaks and gear things, you cannot get new ears.