O2 should be pretty cheap. i'm thinkin i may go get a 5lb cylinder (or a 2.5lb if they carry them that small).
initial cost of the cylinder may be around $25-$50, but the actual cost of the O2 on refills shouldn't be more than a couple bucks. and should last you a loooooooong time if shipping is all that you use it for.
it does work and help alot. i normally just blow air into the bags before i tighten them up, but we exhale CO2 mostly....
i would like to see an experiment done with putting O2 in a bag, and then compressed air in another bag (gas that contains nitrogen and O2). i wonder if there would be any difference.