1 The total cost for a basic 200-square-foot screened-in porch will range from $766 to $1,025 or an average cost of $4.48 per square feet. 2  The cost of materials for a top-of-the-line screened-in porch on an existing deck runs between $860 and $1,070 with an installation cost between $297 and $304.n average construction estimate for a completely new screened-in porch is about $70 per square foot. Therefore, a basic porch (8-foot by 10-foot) with a roof and screen measuring at 80 square feet would begin at a cost of $5,600.