No need to go totally out of pocket. My respiratory guy hooked me up with a medical equipment supplier. I called the supplier and asked which units they had that would fit the prescription. By the time I went to the supplier, I knew which one I wanted. The out of pocket part was the DC cable, totally overpriced for a hunk of wire with a fuse and connectors. I think I got the cable on Ebay.
Respironics is one that operates on 12 V with no converter or inverter, and therefore no converter or inverter losses.