timdorr
Model S P90D w/AP3.0
I believe SCs are ten 10KW chargers in parallel. If a second 10KW charger on board is a $15,00 retail option then it would be logical to think SCs are about $15K retail per bay.
No, power systems don't scale like that. It's a single on-site transformer (likely owned by the power Co and leased to Tesla) that converts the AC on the service line to DC. That's then switched and fed straight into the Supercharger, which dumps it straight into the vehicle. That switches off the internal charger power rail to a dedicated rail (this is the Supercharger hardware) that feeds that into the batteries evenly and safely.
While it may seem economical to just hook up some parallel chargers, generally its easier, more reliable, and even cheaper to just run it through one giant transformer instead.