The Discover Maine Rail Pass can be used for 10 one-way trips on the Downeaster between any two Maine stations within 7 days. Cost is $19/person.
Maine Amtrak stations include Brunswick, Freeport, Portland, Old Orchard Beach, Saco and Wells.
Looks like a pretty good deal, but the online ticket-buying process is clunky. Don't wait until the last minute to book.