Lowe’s has ChoiceDek 16-ft Beach House Gray Grooved Composite Deck Board for $7 per board in some stores – YMMV
I just picked up 75 of these boards for $6.30 each after the 10% off coupon in 16510. There are several stores around that area that have them as well. I ordered them online with delivery, as long as you change your zip code to the right area they show up as the clearance price.
There are also some of the 12 foot boards for $5.25.
16 Foot: https://www.lowes.com/pd/product/50083930
Brickseek: https://brickseek.com/lowes-inven…u=50083
12 Foot: https://www.lowes.com/pd/product/3612030
Brickseek: https://brickseek.com/lowes-inven…ku=3612