My girlfriend and I stayed 2 nights at Santorini Guesthouse and had an excellent time! We had a rental car and there's parking across the street, a 2 minute walk away and literally right at the base of the Sunrise Peak. Our second day, we woke up early in the morning and walked there and enjoyed an early hike, almost entirely empty of other hikers. Highly recommended.
The guest house is also a short 5 minute drive to the ferry to Udo which we also highly recommend. The hosts will drive you there if you don't have a car and if you get up early enough.
The rooms are very simple but very clean. The hosts are extremely nice and cook breakfast for you in the morning. They also have a very big, very fluffy, and very friendly dog Momo. I 100% recommend staying here. If I do ever come back to Jeju, I would stay here again!