An interesting route would be to travel by bus from Medan to Berastagi and then take another bus to Tongging. A ferry runs, once a week , from Tongging to Ambarita. I haven't used this route. I found Ambarita to be a bit too quiet and remote. The food at Tuk-Tuk is good and much better than at Medan or Bukit Lawang , the portions are sometimes a bit stingy.
Some places can even make good Pizza.
During 1999, a room with a lake view, attached bathroom and running hot water cost about Rp30,000 per day. A meal cost between Rp10,000 to Rp20,0000, a Pizza cost Rp25,000. A seat on a tourist mini-bus from Medan to Toba cost about Rp30,000, using public transport would cost about Rp10,000. A visit to the hot springs on the western side of Samosir Island is interesting. Other activities include trekking and cycling.