I have made tall plastic rings from 1-gallon plastic jugs before, which work okay for camembert type molds. Cut off the base and the top. The thinner, translucent plastics from e.g. vinegar jugs can be a bit too wobbly, but thicker plastic from (in my experience) maple syrup or molasses jugs works okay. Hardest part is getting an even, level cut all around. Can also poke some holes from the inside-out for extra drainage as well.