re: companionway hatch for a boat

In my area a good substitute for red cedar is yellow (Alaska) cedar. It is harder, stronger and equally rot resistant. However that is in the Pacific Northwest so I don’t have any low cost options or even marine plywood sources for you in your area. You should be able to do some google research on the topic and find a nearby supplier.
My second choice after teak would be Honduras Mahogany but it’s not exactly cheap either. Unfortunately boats require good material and it just isn’t cheap.
Sorry I can’t help more.