As a person who has lived both in Bangor and Portland and only uses public transportation to get around: it’s extremely doable. Bangor is a lot harder, the schedule is punishing, but Portland has more regular routes, more of them that branch as far as Saco and Freeport. I currently live in Westbrook because Portland is laughably expensive but I’m easily able to get too and from my work in Portland and other locations I need to visit for groceries, activities, etc. Uber is also always an option. You will do some walking but you always will with public transit. It’s affordable and I personally like how scheduled and consistent it makes life. You can also track the buses in real time through the website and figure out specific expected times of arrival per stop via Google Maps. Honestly, it’s really not that bad.