NEXT STEP. Find out how much your project will cost. Provide a few details about your project and receive competitive quotes from local pros. The average national cost of building a foundation is $7,775, with most homeowners spending between $4,239 and $11,710.This data is based on actual project costs as reported by HomeAdvisor members. Any structure, whether a house, a garage, or workshop, is only as strong as its foundation.ind out how much your project will cost. Provide a few details about your project and receive competitive quotes from local pros. The average national cost of building a foundation is $7,775, with most homeowners spending between $4,239 and $11,710.