The standard medicare (and most insurance) policy is to have you rent the CPAP machine for the first several months (13 for medicare, 10 for many private insurance carriers) and you do not own the machine during that time.
If I understood correctly, my Insurer rents the machine for the 3 month "trial" period. Over the next 9 months they pay for it and then at the end I own it. I'm 100% covered so I don't see anything on the money end.