I set up my O2 system for $160.
I bought a new Luxfer 415 Liter tank on eBay, and bought the valve, pressure gauge, and regulator new from Cramer Decker Medical out of California. The regulator is a CP540-4, which is a compact, single-outlet pediatric unit with low flow. I lucked out on a new Nelson A-3 flow regulator (eBay), and a Oximizer cannula (new, also on eBay).
Following instructions from Catalina Cylinders, I valved the O2 cylinder myself, and made up a complete label for the cylinder, using the same data & graphics (e.g. the "universal" Oxygen caution symbol) that would be shown on a commercially-integrated aviation O2 cylinder. In addition, I indicated on the label that because of modern production techniques of O2, filling with Aviator's Breathing, Welding, or Medical O2 was acceptable.
Works well. 16,500 feet at 4.2 GPH & 155 knots groundspeed is a treat!
I have not made a permanent mount system in the VariEze yet, but will get to that eventually.
For what it's worth,