Approximate costs...

General costs of the trip is around 48,500 Baht which is consisted of :

1. Plane ticket - 20,000 [round trip]
2. JR pass - 9,000 [7 days]
3. Accommodation - 9,000 (1,500*6) [6 nights]
4. Food - 7,000 (1,000*7)
5. Entrance fee - 3,500 (500*7) [visiting places]
   

The number can be a little bit lower in a super economic plan by reducing standards in accommodation and food, but I think it is not worth sacrificing comfort and satisfaction just only for a small amount of money and it already is an economic plan. However, leveling it up is at your request, while timing and number of teammate could also determine the price.