The cost of materials for a basic 200sf screened in porch on an existing deck in most urban areas should run between $470 and $680, with an installation cost between $296 and $345. The total cost for a basic 200sf screened in porch will range from $766 to $1,025 or an average cost of $4.48/sf. 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.