Does anyone here know how the upgrade works for Hertz?

I'm a President's Circle member. I rent often from YVR and YVR-area HLEs. I usually book B/C and get upgraded to C only. Regardless of my rate class (B,C,F), I always get quoted $20/day at the counter if I want to get a Camaro, Mercedes C300 or Volvo XC90.

The same thing applied to my friend when he booked a C and was quoted $20/day by the YVR manager for the XC90.

Do other locations charge $20/day for a premium car, or is it just YVR?