The project cost of retaining walls Hoquiam may vary depending on the materials to be used, labor and accessibility to the site here the wall will be built. Using pre-cast interlocking concrete stone blocks which lock together without using mortar is the most modern type of retaining wall developed. Its cost run between $15 to $30 or more per square face foot or approximately $750 to $1500 for 30 inches high and 20 feet long wall. A wood retaining wall can cost you $20 to $25 per square foot which place a 50-square face foot wall between $1000 to $1300.