A single hotel room always book ahead for weekdays should cost you from around 800 kr and up special offers are common and cheaper, but you can find reasonable cheap lodgings in camping huts 300-600 kr, space for entire family, mountain cabins 150-300 kr per person, youth hostels 150-250 kr per person, etc. Most of these will require you to make your own food, bring your own bedsheets, and wash before leaving.
For longer stays one week or more consider renting an apartment, a house or a high quality cabin. Several agencies offer reservations on houses or cabins owned by farmers or other locals. This type of accommodation is frequently more interesting than a standard hotel.