We could make a valved rear muffler for half that...
As the GT86 doesn't have a valve as stock you need a system that will let you choose between quiet and loud mode.
You can purchase a compatible electro-pneumatic valve (to be fitted on the intake so it'll give you a vacuum line) + switch (or even a remote) + vacuum pipes for less than $ 300.
This will control a pneumatic valve on the exhasut and will allow to between loud and quiet mode at will.
We don't use electrical valve as they are prone to failure caused by heat.
Aso for the design, the loud mode can be a direct pipe, the silenced as quiet as our homologated system.
Both modes can discharge through the tailpipes, to avoid bypass pipe that send the gas under the car as some cheap systems does.
This is for the TT-RS, perfect left-right split in both modes:
The valve is made by HJS (which provide our cats) and has its own heatshield.
This is how the sound changes...