You could do a custom piece by piece but I think you'd still spend a little over $3K just for the kit. Most of the parts are available through Nismo. If you only want to spend $3K I'd just get the DET without all the other goodies like the JWT ECU.
Unless you can get a DET with the JDM maf and ECU you will need a JWT ECU. The BB ecu won't run the stock DE's maf. AFAIK the BB det maf is a real hard thing to find and good luck if you do get one and its no good.
I'm not sure if JWT will program the ecu for the cobra maf and the 370cc injectors. You would have to ask them. BTW the cobra maf is freakin huge! The inlet side is a good 3.5" wide then it looks like it necks down to 3".
I think I'll probably end up just saving up
and blowing all that cash on everything at once... breaks and engine. I guess I can afford to wait another one or two months so that everything runs perfectly. Less worries for me when I get the car running.