Hotel Aventree Busan <-- this hotel is newly opened in March 2014 and have family room, approx. HK$1010/room/night for family room in Agoda.
The comments in Agoda, hotels.com & trip adviser are good. Located next to Nampo shopping area and PIFF square, it situates near the Jagalchi metro station and it will take 5-10 mins walk to the hotel.