Well your looking at £4661.60 for the Stillen charger kit, then you'd need the Stillen strut bar as you can't use the OEM with this kit (no idea on price of that), then you'd also need some supporting mods like bigger injectors, higher flow fuel pump, possibly a fuel pressure regulator, plus fitting, plus remapping, etc etc.
I'd say budget around £7K to £9K tops although could be done a little cheaper "maybe".
Incase you want to put it on your credit card available here: http://www.tarmacsportz.co.uk/GB/350z_STILLEN_Stage_3_Supercharger_System/350Z-407350IC3_.aspx