No no no no no i'm not saying you have a fuelling problem, among the problems i also had very poor starting, had to start it a few times when cold, but when hot........OMG u had to crank for about 5 mins because of the lack of fuel pressure.

To test the servo:

firstly run the car, and push the brake pedal and switch off while depressing the pedal, and you may feel the pedal pushing your foot back up,

second test, run the car, switch it off, pump the pedal (u should hear sucking/air noises) and the pedal will get harder, do that a few times then hold the pedal in and re-start the car and the pedal should go down a bit once running.

If u can feel the pedal forcing your foot up on switch off, and if there is no vacuum noises doing the second test then the unit isn't holding the vacuum and has an air leak.

U should also be able to pull the pipe off the servo and hear whether its retaining the vacuum pressure or not, i bet it doesnt if your getting this wheazing noise.

The tiniest air leak on the KE system causes MASSIVE running problems, i fucking hate it, it pisses me off, im going EFI end of story end of problems everyones a happy easter bunny

As for prices, i really don't know, i bought a cossie break kit ages ago off ebay and it had a literally brand new servo with it all, my old one was completely fucked though, it was the original one though it had done well, 21 years of service. If ford dont stock them anymore u will get a third party one.