Greddy kits are cheap now since there are many other companies make a kit for D16s. Actually, it will still be hard to find a GReddy turbo kit
with intercooler for $1500 but it is very very possible on ebay. You can even go to
www.homemadeturbo.com/forum and get a used custom (not a pre-fab kit) for less than $1000 with intercooler. As far as HP gain, your boost pressure and
tuning directly controls that gain. The rule of thumb is 1 psi is equal to 8-10 HP gain with tuning efficiency. The GReddy kit comes with a stock internal wastegate setting at 5.5 psi... so do your math..... approximately 50 more or less HP but a noticeable gain. I would like to emphasize what nonov said about the fuel management. I've gone thru every BASIC way to manage fuel to compensate with boost. It is the most annoying task. The GReddy blue box sux arse. The boost dependent FMU sux cuz the N/A to boost transition bites and is not really healthy for your engine. Go to my website and learn most of the basic stuff
www.thermal99.com. Another thing to keep in mind is that, your 00 civic has an OBD2 ECU. This ECU is very sensitive to sensors which makes it hard to tune with turboed Hondas. I'm getting ready to switch to an OBD1 P28. Lastly, Hondaman-iac sells all kinds of turbo kits. He gives discount to members here. Goodluck.