Plastic Lumber
Deck planking
1" thick, 5.4" wide
http://www.lowes.com/pd_371959-46086-212678_1z11px3Z1z11kdvZ1z0yshqZ1z129cq__?productId=3612028&pl=1 $15 for 8' length
2x4s made from recycled water bottles
Plastic lumber is "Actual size". Plastic wood premium grade only for 2x12. Rest is available as utility grade.
http://www.american-plasticlumber.com/sizes.html
http://www.american-plasticlumber.com/structural.html
http://www.epsplasticlumber.com/index.cfm?fuseaction=page.bear_board
See what is available from HomeDepot and Lowes for decking.
Plastic tongue and groove
1 x 6 T&G 3/4" x 6"
2 x 10 T&G
1-1/2" x 9-3/8"
2 x 12 T&G 1-1/2" x 11-1/4"