supporting 400 and making 400 are vastly different things. and do my research? i have owned 5-6 z31's in the past 5 years, ontop of the fact that i have been around z's my entire life. i KNOW what it takes to get power out of a z31 and take a helluva lot more then you think, like i said, it takes more then a boost and a tune to make power.
lets do a cost estimate for a stock internal'd vg30et this is to say make a low balling 300WHP at 13psi.
1: gutted plenum runs around $300
2: 240sx 60MM TB ran for around $70 last time i checked.
3: nistune, with all the required nistune stuff is $530
4: wideband and gauge innovate motorsports XD-16 retails for $375
5: hotter/colder plugs and bigger wires with a MSD blaster coil, $136
6: cheap-o ebay generic intercooler kit, $300 plus whatever misc elbows and piping you need.
7: turbo, garette GT35R (holset's dont like large boost #'s) around $1100
8: timing belt kit, with new water pump, seals, tensioners,..etc around $400
9: down pipe for the turbo $200
10: wastegate (because boost spikes kill) $300 for a quality used one (TIAL, greddy..etc)
11: cheap BOV around $150
total= $3861 building a fast car or high HP dyno queen never is and never will be cheap, if you want something you can build cheaply go buy a honda.
and that is about what you need to PROPERLY boost it.