More mustang horespower?
A single turbo will cost more then a supercharger. You wont be able to get to 350-400hp without getting a supercharger or turbo charger or doing some serious re-building of the engine. You can probally make it to 325hp with just the basic mods. You could do exhaust, underdrive pulleys, cold air intake, and a sct tuner with a custom tune. You could get all of that done for around 1,000-1,500 and it will get you to around 325hp. There is not much more you can do after that, there are gears but you really dont want to change those for a car that is used to drive on a everyday basis. Take a look at Eaton superchargers, they make a roots type supercharger for a descent price, there is also vortech which makes a centrifugal type supercharger. They are a little more expensive then Eaton but you will get more out of there superchargers.