On the subject of o2 on the cheap, anyone remember this event?
Many years back a glider pilot, rather than buying overpriced o2 from British Oxygen Company, snitched a refill of his bottle instead from a mate's Oxy-Acetylene kit.
Piloting his glider in epic wave lift, all went well until he crossed the magic 10,000' mark and turned the kit on.....
... to find out with the first breath that he had filled his bottle from the Acetylene side rather than with o2.
This story is many years old and I'm sure apocryphal