We took $1 store aluminum water bottles, flattened the plastic cap, JBwelded the threads to seal them, tapped the cap 1/4"NPT for a nipple and put a breather in the other end of it.

We were down to ~$3 or so for an "aluminum catch can". Kinda hard to see, but if you put a sticker on it, it makes it look like a $20 catch can.