RE: Amtrack and buses...
Yes, Amtrack runs the Downeaster to basically Portland. Concord Trailways is a convienient bus line that runs up and down the east coast. They do have an "express" route and a "local route" the Local route is awesome but of course, slower as it goes up Rt 1 through Bath/Brunswick/Rockland/Belfast/Seasport, etc. etc. And the express route basically goes inland to Bangor/Augusta. Greyhound also runs up and down Maine. Concord I think is convienient cause they have a depot at the train station. Greyhound I'm sure must also go there but I think there is some affiliation between the Amtrak and Concord Trailways as I remember looking at the websites last year about that.
Maybe you could hit a ride on the many RVs that head up the coast??
Taking the local route is really fun. I've taken Concord trailways from Belfast to NYC before and by sitting on the driver side of the bus, I got a complete view of the coastline and saw many places I'd like to kayak!
The bike shop in Exeter, NH that we stopped at is
Exeter Cycles Bike Shop
4 Portsmouth Ave
Exeter, NH 03833-2106
Phone: (603) 778-2331
Nice guys and a nice shop. It's also convienient if you're trying to do a cross-Maine trek because they are not far at all from the NH-ME border. You could ship the bike to them and then pick it up when you get there.
Jay