90 has tolls from end to end but Massachusetts got rid of the booths so there is no stopping. You will get sent a bill. If you have time a brand new MGM casino opens in Springfield, MA on 8/24. Less than a mile away is the Basketball Hall of Fame. If you go through MA, most people get off 90 and take 495 to 95 for Maine. You should see Boston if you never have before. Don't take your RV into Boston.
Many people coming from your direction jump off 90 around Albany, NY. Burlington, VT...then Ben and Jerrys...White Mountains of NH and then cut across to Maine. Day trip/s to Bar Harbor is a must. Watch the harbor around Searsport. We saw purpoise and seals. Go on a whale watch or a harbor tour.
Another option to reduce tolls is to take 70, 71N Columbus, 76, 80, 81, 84, 90, 495. You will bypass Niagara Falls though.
Have a great trip.