if you just want to lower, eibach prokit on stock shocks, 150-175 for these springs. lowers 1.5 inch on stock.

if you want performence, 300 wont be enough, even on the lowest budget, you are looking at 550 plus at least just on parts. (namely, kyb agx with neuspeed/eibach springs), while higher end ones will cost in the range of 900 (tein, apexi ws, koni sports shocks with spring/coil of your choice...)