Portland, Maine by way of Boston, Massachusetts
If you're looking to fly into Portland, Maine (PWM) and finding the price a bit steep try flying into Boston, Massachusetts (BOS) then taking the shuttle bus from Boston Logan airport to the Portland, Maine bus terminal - which happens to be next to the Portland, Maine Amtrak station as well as walking distance from downtown. I've taken this route ei.ther to save money or to have flight times that work with my schule better. The airport shuttle usually takes 1 hour and 30 minutes but make sure to factor in traffic for the just in case scenarios.
Another alternative route is to fly into Manchester, New Hampshire (MHT) then taking the airport shuttle to Portland, Maine. I have yet to take the route though.
Shuttle Bus links:
Train: