A good option for many travelers is one of the several dozen vacation rentals; rentals range from tiny cottages at less than $100 per night (minimum stays are often required, especially in summer) to large homes that can host groups of 10–12.
Check with the Seaside Visitors Bureau, or contact one of the rental agencies: Beachhouse Vacation Rentals (503/738-9068, www.beachhouse1.com [1]), Oceanside Vacation Rental (503/738-7767 or 800/840-7764, www.oceanside1.com [2]), or Northwind Vacation Rentals (503/738-5532 or 866/738-5532, www.northwindrentals.com [3]).
Links:
[1] http://www.beachhouse1.com
[2] http://www.oceanside1.com
[3] http://www.northwindrentals.com