Average Cost per square foot for Garage Floor Epoxy Painting in Granite. The average cost to Epoxy Coat Garage Floors in Granite 2015 is $1.27 to $2.35 per square foot. Always make sure to make all hiring decisions carefully and to make sure the contractor is fully insured, bonded and licensed.It is a good idea to check references and verify prior work quality.he average cost to Epoxy Coat Garage Floors in Granite 2015 is $1.27 to $2.35 per square foot. Always make sure to make all hiring decisions carefully and to make sure the contractor is fully insured, bonded and licensed.