Interlaken has a wide range of hotels in different categories. 

Homepage Tourist Office Interlaken: www.interlaken.ch

Here are a few recommendations, especially for groups:

Homepage

Prices start at CHF 43.00  pP (group accomodation for 6 persons, shared toilet/shower on hallway)

Private twin bedroom with en suite bathroom available.

Included:
breakfast
sheets (all beds made up) and a towel
private lockers in all rooms
use of self catering kitchen: 24 hours
high speed WiFi in the whole building and all rooms
free entry to public in- and outdoor swimming pools
free Minigolf and Tennis
free use of public busses
parking
all taxes

Homepage

(For young people who enjoy the nightlife)

Alpenblick (right at the lake of Thun) offers group accomodation in tents: Homepage

Manor Farm (right at the lake of Thun): Hompage