How is buying a kit that comes with the right parts that you want ever going to be cheaper? If you piece everything together its always cheaper if you were to basically get the same parts that come in a kit. Parts for a rx7 arent going to be more expensive than any other car except maybe the turbo manifold, downpipe, and chargepipes....and even then the downpipe and charge pipes can be easily made yourself or if you know somebody that can weld . The turbo isn't vehicle specific, neither are the injectors, neither are the bov and wastegate, couplers, intercooler, etc.

If you go through and piece together a nice kit that has all the right parts for making good power it may be more than a simple kit, but at the same time should be a much more quality setup. Also remember most kits dont come with some good engine managment. That also ends up being real expensive in some cases, but is worth it to save your motor.