There was a price increase just last month for California superchargers. I pulled this from an article on the matter:
"peak hours will now cost $0.58 USD per kWh instead of $0.48 USD per kWh, while off-peak Supercharging (which is typically priced lower) will be billed at $0.29 USD per kWh instead of $0.24 USD per kWh."
So I guess if you charge off-peak at a SC you could save a few bucks.
Sadly, with the Diablo Canyon nuclear plant likely going offline in 2025 (there's still some debate it seems on what PG&E / CA govt are going to do) I think rates are likely to keep going up in the coming years.
EDIT: Quick thought, you might look into what other charging companies are charging like Electrify America, EVgo, Blink and others. Use plugshare.com to see whats available near you.