Make mid-summer reservations as early as possible; many of the rooms book up six months ahead of time for weekends in July and August. Winter rates are often 30 percent lower than the listed summer rates.
In addition to the places listed here, the Chelan [1] area has many private vacation homes available; the Lake Chelan Chamber of Commerce keeps a complete list, and also keeps track of motel availability in the summer.
Links:
[1] http://www.moon.com/destinations/washington/north-cascades/chelan