First, I'm glad everyone had such a great time visiting Acadia/Bar Harbor! I live just outside of Bangor and I used to work in Bar Harbor- I'm just happy everyone had such a great time here!
How about southern Maine? Every August we rent (airbnb or vrbo) a cottage in York. It's not cheap, but it's way cheaper than hotels. York has beautiful, white sand beaches. Downtown York Beach is a bit tacky, but it's good, touristy/tacky. There are several breweries in town, if microbrews and live music are your thing. From York i's about a 10 minute drive south to Portsmouth, NH. I LOVE Portsmouth! There are incredible restaurants, history (visit Strawbery Banke), music and plays (check the schedule for Prescott Park), shopping, etc. Portland ME is about 45 mins north of York, Salem, MA is about an hour south, and Boston is about 90 mins south (depending on the traffic, and you can always drive to one of the 'burbs and take the T into town- that's the subway/train system). You could alternate beach days with travel days, and if you want you could even head to Salem, NH, and go to Canobie Lake Park for the day.