You'll likely find much you prefer. Despite ones best efforts, the chosen hotel sometimes turns out to be unsatisfactory. The local tourist office can be a big help in locating alternative accommodations. The Internet has made finding hotel recommendations remarkably easy. The Eiger Guesthouse has dormitory rooms and twins without bath for excellent prices with the convenience of a hotel.
Breakfast is pretty slim, but the owners get high marks for being friendly and attentive.
M rren's Tourist Office, for one, provides a brochure of apartments for vacation rental. Most other town TOs will as well. If you give the dates in which you're interested they'll supply a list of apartments available during the period. You'll find several campgrounds in Interlaken, Grindelwald and Lauterbrunnen. While you can find bargains, they're relative, and the traveler accustomed to cheap lodgings in Southern Europe should expect to pay more.