it will make 350whp with bap but not 450
walbro will not work in the focus unless you switch to the return fuel system. the stock pump voltage is varied to maintain proper fuel pressure and flow instead of the pump being ran a consistent speed and the excess fuel being returned to the tank. this will not work with the walbro b/c it will wear out the gears inside the pump, it was designed for constant gear speed not variation.
the price of this would depend on how you go about doing it. some use stock tank with a return line and other things trying to get it to hold fuel at the pump with 1/2 tank. some switch to a fuel cell to avoid the fuel starvation problem at 1/2 tank
i may also be working on a surge tank set up very soon.
read through this