Probably too late for the OP but might be of interest to others. Most relevant information will be found at Hurtigrutens own website . The term for port-to-port is Distansereise, and this can now be booked online, including cabin and food. Living in Kristiansund, one of the ports for Hurtigruten, I am a fairly frequent passengers, especially on the northbound (Nordgående) Kristiansund-Trondheim sailing.

Generally summer is much more expensive than winter. Prices are comparable with flying, but the experience is worth it. On my typical journey; KSU-TRD in winter, I usually pay around NOK 750 including a single cabin, for a seven hour trip by night. (There are no flights; the daytime catamarans are NOK 435 which is about the same basic price, i.e. transportation only, as the hurtigrute.)