CPG Seaboard is a competitive product and it was a little cheaper than King Starboard. I bought some years ago from a company that was selling scrap pieces on eBay, but I can't find the name of the outfit. When I Googled it, a sponsored ad came up and I clicked the link:
http://thecuttingboardfactory.com/Me...egory_Code=4MB
Just be careful. Starboard is High Density PolyEthylene (HDPE), which can come in lots of formulations. One characteristic of marine-grade HDPE is that it has UV stabilizers. So while using a HDPE cutting board for a hatch might be economical, being exposed to the sun as it would on a boat would compromise it's physical properties from the radiation.