I would say that you might want to check a local surplus store. They might have something for a reasonable price that you can use as a starting point. Like a M1 helmet liner or something.
I once shot a squirrel thinking it was a grey squirrel, because they were supposedly carrying some kind of disease at the time. When I turned it into the DNR for testing (and a reward), I was informed that it was a yellow squirrel and endangered. Oops.