Stroika Concrete makes bags of easy use concrete for the DIY market. The company mixes their concrete using two ingredients, "Great Grit" and "A1 Aggregate". Great Grit costs $1 per kilogram and consists of 20% fine sand, 40% coarse sand and 40% gravel. A1 Aggregate costs $0.75 per kilogram and consists of 10% fine sand, 50% coarse sand and 40% gravel. Each bag of Stroika concrete must contain at least 2kg of fine sand, 2kg of coarse sand and 6kg of gravel.

What is the least cost combination of the ingredients that will satisfy the minimum requirements and what will be the cost of these ingredients per bag of concrete produced?