While I dont know for sure, I am fairly confident that there will be some kind of free or moderately-priced transpoetation between ship and downtown.
DisneyCruise lines are such a classy operation, they regularly offer a free bus unless the port or town provides its own (typically low-priced) alternative. I don't know if this is official policy, but I have seen and used their buses regularly (Tallin, Estonia; Juneau, AK; Stockholm, Sweden; etc.). In Skagway, AK, a town bus costs $2 and in Ketchikan, AK and Madeira, one docks downtown.
So for me, the best part of DCL, I don't worry; I just enjoy. And I believe that the premium we pay upfront for the cabin/cruise is more than compensated by the many "extra 's" that seem to keep coming.