The price is not a joke, but food pics means high cost price such as meat are not using so many.https://www.hokke.co.jp/wp/wp-content/uploads/2015/07/b8869842b8e620e3...
But the center food is "fried chicken", this is one of poplar local food in Oita prf, not only in Oita city.https://www.oishiimati-oita.jp/en/#food
Although it will be enjoyable enough at that price, this price is only in the country and possible to do,
it does not mean that you can find that price buffet(食べ放題 or バイキング) everywhere in Japan.
Anyway, in the Oct of next year 2019 sales tax will re-rise from 8 to 10%,
but if the purchase price of the ingredients goes up before that,
or if the Chinese with bad manners are targeted this project will end soon.
What is the lunch menu??
Weekday lunch buffet 800Y. (closed on Sundays and natinal holidays)
Business hours will be 11: 30-14: 30 (14:00 last order), some busy season will not, 70 seats.
2 daily menu and as a standard menu salad, sashimi(raw fish), pasta, nimono(boiled), fried, egg, tofu, washoku(Japanese food), special curry, noodles, rice, local dish, bread, homemade jelly, fruits and a large number such as 2 kinds, zenzai, cake, icecrems, several kinds of drinks, also desserts popular among children and women.
So it would be fine just for lunch, but you should consider it separately as a hotel to stay.
You should use contact form.https://www.hokke.co.jp/english/contact/?viewhotel=oita