Dilley,depends on what system you go for ,i,ve been through the hole thing and i tell you go for it the benifits are big ,my system cost just over 3k including all the mapping ect , and yes before you ask it works 100% (note to factory)
For me (Carb to EFI) was around £2200+, that was with no labour and no outside tuning. I kept the cost down by doing everything myself, but did use expensive Aeromotive stuff and lots of Earls pipe fittings.