In 2010 we stayed at Timberland Acres rv park in trenton which is about 15-20 minute drive to Bar Harbour .You might hit it lucky as we got a special rate for the month of May at $25.00 per night full hook up s and cable. You will find that anywhere close to Bar Harbour can run you up to $75.00 per night in hi season
Timerland is not fancy but great folks running it and gets good reviews on RV Park Reviews web site. Lots to see and do in Bar Harbour area loved Acadia National park
Unhook and take a drive up cadillac Mountain you can see for miles. Didnt go to Portland area but again check RVpark reviews.com
If you get up near Camden stay at the Camden state park campground its nice.
Hope this helps
Bill