You wont be able to twin charge for less than £10k. Hell, Id be surprised if you could do it for sub £20k.
By the time you include Fuel return systems, exhaust, mapping.....
Give Mark a call at Abbey Motorsports and go from there.
and as I already said - go to my350z.com. Do lots and lots and lots of reading. Everyone who has gone FI here (and there aint many) have got knowledge from my350z.com.