What part of “use premium only” is unclear to you? If that is what the car’s manufacturer specified, then that is what you need to do, unless you want to risk damage to valves and pistons. Additionally, if you do use regular gas, it is likely that your fuel economy (and your performance) will be degraded sufficiently to negate the cost savings of regular gas.
So, I would suggest that you “do the math” involved in the issue of paying a couple of dollars less at the pump vs. probable lower gas mileage and reduced engine performance + a serious risk of damaging the engine.
If the car’s manufacturer specified premium gas only, using regular gas would be a very good illustration of being “penny wise and dollar foolish”, at least IMHO.