Mxsmanic wrote:
I am curious to know how many GA pilots always have oxygen on board,
even if they don't normally fly at high altitudes. It seems like it
would be good to have around, but I don't know how much it costs. Do
oxygen systems have to be frequently topped off or inspected or
measured? Do they just consist of masks for passengers and pilots to
wear?

Per FAA and other rules, O2 containers must be checked and certified
every 5 years. Refilling the tank varies depending on the FBO doing
the refill.

Oddly enough, I am unable to have the tank refilled at a medical
supply shop because I don't have a prescription for O2.

www.mhoxygen.com
www.aerox.com
www.c-f-c.com/supportdocs/abo1.htm
www.aviationoxygen.com

for details.