I went through a similar problem with my SI not long ago. I had a stroke in 2016 and the neurologist ordered a sleep study. The study came back just above the FAA limit at 18.7 but the doctor never prescribed any CPAP therapy. When I sent in my SI application the FAA said I had to have therapy because I was above the 15 AHI limit. Since it had been a year and a half since the first study, I did a in home study with RPM (rpmhst.com) due to the cost of a in lab study and it came back positive too. I paid $150 for the home study and around $600 for the Airsense10. They do not take insurance, but will do $300-$325 depending on the machine and $50 a month for six months. Be sure to sign up for their email specials, that saved me another $100 on my machine. It also comes with a free mask of your choice (I like the dreamwear because the hose is on top of your head not your face and causes less disturbance at night if you toss and turn in your sleep) plus lifetime monitoring, just be sure to tell them it for the FAA, they had to change a few perimeters on mine from their normal CDL setup. Good luck, as long as you do what the FAA requires for usage, you should have no problem.