...Reminder, if your car's manual does not state that you need Premium, there is no benefit in using it. It isn't 'better', it's just different in a way that only helps if the engine is designed for it. If not, it's just a waste.-ERD50
True....however, I would remind other folks that it is recommended to check your owner's manual and find out what octane level is needed for your vehicle.
" If you use a lower than recommended level, the gas may combust too fast for your engine. That can cause the engine to make a knocking noise. In addition to this unwanted noise, a lower than recommended gas can also reduce your car’s power and fuel economy and cause engine damage. "
https://www.communitysure.com/blog/understanding-premium-vs-regular-gas/
To answer the OP's question, the difference in the San Francisco Bay Area averages 30 cents between regular and premium. We don't drive much so no big change in our monthly gas bills now that we have an SUV that takes premium-only.