For those who are traveling to Maine, we recommend that you fly to Boston Logan International Airport (BOS).
For maximum flexibility to explore New England, we recommend renting a car at BOS airport, then drive to Augusta, ME. The drive is about 2 and half hours, and it's a great scenic drive to soak in the sights and vibes of New England. Maybe stop by witchy Salem that’s just north of Boston.
Alternatively, checkout https://www.capeair.com/ for flights between BOS and Augusta State Airport (AUG). Hertz is at the Augusta airport for your rental car needs.