Remember, a 2x6 board is a 2x6 in name only. In real life the board is 1.5" x 5.5". The six pieces will get you 4.5" of height.My local Home Depot has 2" x 6" x 8 ft boards for $4.98/ea. If I cut them 16 inches instead of 18 inches I get 6 pieces per board.
Doesn't seem too bad....