Local brew club, huh? Ames area here.
Some, I understand, use a balloon with a pinhole in it for an 'airlock'.
I have 40 gallons of home-pressed cider in the freezer in plastic gallon milk/water jugs. The two-year old stuff brews up nice and clean, as if the plastic didn't let too much through, so I'd wonder if a person might ferment on the cheap in those.