They're more expensive, but if you can get a ResMed version that has the auto setting, that'd be your best bet. It'll go up to 20 pressure-wise, and then it doesn't need recalibrating, it just uses computer magic to figure out what pressure he needs right then. They're about $2k, but well worth it.

ETA - See if your local chemist does the testing. That's how I did it, I had to wait a week for a spare test machine, and then got the results within 10 days. I have severe apnoea (116 per hour!), so they got me a rental ASAP and let me keep it until we could get another machine.