Inexpensive Teak does not exist
Teak is not cheap, period. An alternative is polycarbonate sheet(Lexan) or Acrylic sheet (plexiglass). You can buy either in 1/2" thick and machine it with regular woodworking tools. It also lets in the light. Polycarbonate is very strong, but not as strong as teak. Polycarbonate tends to craze over time, and the acrylic won't. The acrylic is more prone to scratching and is not as strong as polycarbonate. I can't seem to find polycarbonate in a dark smoke gray shade but I can find acrylic smoked dark.Goggle Companionway drop boards and you'll get some ideas.