4-5k? That could only be labour. Not a chance of that being turbo kit AND labour let alone kit/forged engine/uprated clutch/labour.
Here's a breakdown of what I paid.
Used power Enterprise twin turbo kit £3500
New would have been roughly £7000 which is about par for the course for a truly complete kit.
Labour of fitting the kit £3200
Clutch £450
Uprated bottom end £4200
Fitting of bottom end will be £1000 to £1500
Increase in insurance +£500
Decent tyres to handle the power £600
Dyno tuning...and so on and so on.