hayward and scott are pretty good but aint the cheapest. loads of different systems available for the focus and i aint sure what other focus modifiers favoured exhaust preference is TBH.

my car already had uprated suspension, brakes, wheels, blah blah so the supercharger kit was kinda the next thing it needed. once you have the extra power you would need to think about upgrading these things aswell, so total cost do get the most out of it will esculate which all boils back to maybe thinking about buying a beefier model of car to start with...