$50-80 is probably unrealistic for lodging in these areas, especially
in July. For some reason lodging is generally very expensive in the
New England states, even for common motel chains.

As another poster suggested, if you don't mind camping I'd definitely
suggest taking a tent. Not that you would camp all the time, but it
will provide a fall-back option if all the rooms are booked. There are
many National Forest campgrounds and state parks in NH, VT and Maine.
I usually do a combo of camping and rooms depending on the area. In
many places camping is the way to go, scenery-wise! Note that in
places like Acadia and the White Mountains even the campgrounds may
fill up, especially over July 4. Many of them take reservations. In
some National Forest areas "dispersed camping" is allowed; just pick a
likely looking fire road and drive in a ways to set up your tent
somewhere. No facilities, but no fees, either!

Acadia definitely requires reservations, as it's a very popular
destination. July is really the beginning of their tourist season, so
it's bound to be booked. If everything is full, consider looking
off-island in the gateway town of Ellsworth, which offers several
motel choices. It's a 15-30 minute drive (or longer, if the traffic is
bad) into the park/Bar Harbor. If you have time, also consider heading
further up the coast on Rt. 1 past Ellsworth, as most tourists turn
around at Acadia. Campobello Island (which is actually in Canada) is
worth visiting, and the "Down East" coast is still pretty unspoiled
and untouristy compared to mid- and south-Vermont.