$2799, just for the catback exhaust and 20 horsepower (though squeezing 20 extra horsepower out of an n/a 2 liter engine with just a catback sounds highly dubious).
Like I said, opting for stage 1.2 (overpipe w/spherical resonator) and stage 1.3 (header) will be ridiculously expensive.
They also announced a 380 horsepower package. Probably for the cost of a second BRZ.
At this point, if you own Toyobaru and want more power, you really have to ask yourself just how much is that warranty worth to you?