PlyMetal comes in 1/2-3/4-1-1 1/4" thickness with a baked enamel finish (8 colors) on one aluminum skin (top) and a mill finish on the other (bottom). I don't have a source or pricing, but based on the price of Polymetal, I'd hope for $200 for a 4x8 sheet.
VIP Swing Door -- white vinyl on the top, grey HDPE on the bottom
OSB Metal Plus -- Enameled aluminum/HDPE on Oriented Strand Board
Soak the cut edges in epoxy/polyurethane/beeswax.