Do a search on the Congregational Library and Archives Hidden Histories project. This is about early Congregational Church Records online. It’s an ongoing project. You can see a list of mostly Massachusettes towns that are being worked on. It does have a listing for Sanford, Maine since we were part of Massachusettes.
Don’t assume that because your ancestors were poor that there aren’t records of them. Check out records from prisons, almshouses, orphanages, charity societies, and advertisements for runaway indentured servants.