You can try regular gas and see how it runs. Pretty much any car made since the early 90s has ‘knock sensors’ that will retard the ignition timing to protect the engine if preignition (spark knock) is detected. If you notice performance dropping or hear spark knock, then I’m afraid you’re stuck with using higher octane gas. At this point the savings of 10?/gal. are offset by lower mileage you’ll get if the computer retards the spark, and possibly by harm you’re doing to the engine by continually experiencing spark knock if the engine management system isn’t coping perfectly. Also keep in mind that some gas stations’ version of regular or premium seem to be worse than others. My car calls for 89 octane, but I can usually get away with filling up with 87 every other tank as long as I don’t let it get too low before filling.