How long is a bit of string, it depends upon the features of your ECU and everything else you want.

Mine currently owes me around £1200 although there are parts I want to change at present and I expect this will end up in the region of £1800... considering the features and capability's of mine I feel its pretty good value.
How much would all the parts for any other management systems with water injection, air injectors, coil pack, ALS and monitoring capability's cost ?

Likewise another consideration for me personally was how much a competing management would sell for second hand.... A P8 with modified for Dizzyless ignition, Air injectors and water injection along with a pectel monitor and ALS by Paul Hills or EA would sell for good money and quickly