tbh a good quality one is going to cost around the £400 mark.
It's the hardest part of the system to do, and also requires a lot of fitting time, as you need to keep offering it up to the car to make sure it isn't going to hit anything when the engine moves and when it heats up.
Powerflow use 309, ring them, and see how much they will do one for. Oh and i have one of theirs on mine.