The board of chosen freeholders of any county and the governing body of any municipality bordering on the Atlantic ocean in any such county may enter into an agreement whereby the board shall agree to pay to the municipality such sum toward the erection, construction or repair of such works, seawalls, bulkheads, jetties and other approved devices necessary and proper to protect and preserve the beaches and shore front from the erosion and ravages of the sea, but no greater amount or sum shall be appropriated and made available as the county’s share of any such undertaking in any single municipality than fifteen per cent of the total appropriation made available for expenditure therefor.