IIRC, I updated some links on my writeups on that one. It was fairly pricey - c. 10k. Probably good for high usage ops e.g. high alt paradropping. But for private flying, the costs are roughly
$700 for the 48cu ft MH carbon/kevlar cylinder
$300? for the MH 1st stage reg (4 outlets)
$800 for the O2D2 electronic demand reg (includes some cannulas and a mask)
$10? for a plain cannula (x # of likely passengers)
and that's it. That kit will be good for 10s of hours at FL180 for 2 people, so the almost inevitable refill hassle is well postponed.
You need a 540-thread refill adaptor - MH do those too. But I use a hose; details in the writeup.
Given that oxygen doubles the operating ceiling of any half decent IFR tourer, it's extremely cheap. Also the Eurocontrol routings are often much better above FL120.