The cost of a granite countertop will, of course, depend on the size of your surface area. However, the average granite countertop will cost approximately $50 to $100 per square foot. In addition to the size, the cost will also depend on how thick you want the slab to be.he cost of a granite countertop will, of course, depend on the size of your surface area. However, the average granite countertop will cost approximately $50 to $100 per square foot. In addition to the size, the cost will also depend on how thick you want the slab to be.