When you say 'price', do you mean to buy the boat for 2 750 000 SEK, or do you mean the monthly rent: "Månadsavgift: 3.800 kr inkl avlopp och vatten (exkl el)" and "Försäkringskostnad: 1.213 kr/månad (Alandia)"?
It's not a super-high rent to be so central indeed. But I have heard that you need a pretty big boat (minimum 12 meters length, 3 meters width or so?) to be licensed to dock in the city waters? That's probably a big cost. And then I heard there are usually waiting lists of multiple years to get a spot. That's why I was thinking to buy a small boat and find a place some hour away from the city.
Thank you anyway, I will contact the "Djurgårdsvarvets Fartygsförening (DFF)" and ask them.