Yes...and no
The myth "you need to lower the compression when going turbo" is a tough one to get rid of, i understand. because the engine management system and aftermarket systems on the old turbo-cars wasnt as good as todays new cars and engine managements, they had to lower compression.
The mazda 323GTR for ex. is an old turbocar, and it runs a compression of 8,2:1
A new Audi turbocar for ex. is running what? Something like 10:1 or something, as high as a N/A car! This is because modern knock-controllers, sensors and engine management, BOTH STANDARD and aftermarket ones gives you better control of the A/F ratio, timing and firing of the sparkplug, wich again gives you the ability to raise compression for more bang(power)

Therefore, they have more grunt in the low end(high compression to help when the turbo is not spinning, wich again gives more exhaust to spin up the turbo, wich then again, helps on turbolag), and still runs a boosted setup.
If you take a standard N/A engine, turbo it, you must run low boosts(up to 0,6bar) to prevent internals cracking, and prevent wrong detonation, wich causes the engine to seize up cause the original ECU cant keep up, and melts/cracks the piston.
5K£ to reach around 250bhp, with ability to go for more, isnt that bad actually
Im rebuilding my GTR engine(500bhp in a FBG), and i have passed 10K£ a long time ago. Tuning cars are tits-and-arse expencive stuff, simple and easy

If you go for it, you have to commit 100% all the way
But.... 5000£, that sounds like alot of cash just for å turbokit, the price must surely include fitting the stuff as well, or? If so, you can cut that price in half if you do the mechanical stuff yourself, and just leave the mapping/tuning up to the pros
