Mainer here. In fact, I live 1.5 miles from downtown Damariscotta. Small world! Seeing your name makes me wonder if you're mariner?
So, here's my take. It doesn't exist. At least not anywhere that's nice to be. You can get waterfront land for $500/acre WAY downeast. My wife's family is from Addison, and you can find land down in South Addison for a song. Downside is it is 3.78 trillion miles from anywhere. You have to drive an hour just to hit the tiny grocery store in Columbia Falls. That and the road is 3 season. So, unless you drive a tank, you can forget getting to your tiny house in the winter.
That said, you can find lovely houses for great prices in the Newcastle/Damariscotta region. Ours was a deal for $150k in an awesome neighborhood and only a mile from town and a mile from water. There is a bit of land for sale around here, so you could snap up something and build your tiny house there. If you find something, let me know, because I want more than is reasonable to build a tiny house! Or, just be patient and find something awesome that is already built. Either way is a win.
Next time you come to Damariscotta, PM me. Maybe we can have a mini-MMM meeting over a beer at Schooner Landing. :)