Last time I heard, the single supplement for staying solo at Tawaraya was about 20 percent. They let you stay with or without meals. Staying without meals is called Sudomari, and with just the breakfast is called Katadomari, but they have English speaking staff so you will do fine if you call them.

As far as I remember, Tawaraya's rates do not change, except a few days during the new year.

Tawaraya makes beautiful boxed lunches to carry and eat later. The theme of the lunch changes every month. If you are taking a train back to Tokyo after staying at Tawaraya, they are a lot nicer than what you can get on the train.