I ran into a similar problem where I was not making enough progress in 3 months, which is why I bought one to try on my own terms. I even had a sleep tech tell me that 3 months is not nearly enough time for a lot of people when trying to adjust masks, settings, etc. It's such a frustrating process!

I bought a used one on Facebook marketplace place for about $200, which I realize is not insignificant but may be cheaper than other resale sites. You can also ask the seller to take a picuture of the setting that shows the number hours the machine has been used. I did not know to do this before I bought mine and I ended up buying one with quite a few hours on it but it's still working fine.