Here's my favorite place, and you can navigate in English. This ryokan is in Yugawara which is not far from Tokyo. The seashore is nearby, and there are hot springs throughout the area, including an inexpensive park where you can enjoy the springs for 300 yen per person.
This is a first-class inn, so the rates are a little high, but it's worth it. The rooms are all freshly remodeled (many old inns smell of mold and old cigarette smoke), the service is top notch, and the food is about as good as it gets in Japan.
湯河原温泉露天風呂、料亭旅館 | ゆば懐石山翠楼