If you get a mask from a local supplier (a "DME" - for durable medical equipment), it seems to be standard that you rent to buy. I don't think there's a surcharge for rent-to-buy, but a local DME's price will be significantly higher than prices you see on the internet. Insurance pays for CPAP rental/rent-to-buy, without any trouble. The advantage is that if you decide CPAP isn't for you, you can give it back without paying for a piece of equipment you're not going to use. Also, if you need a different type of machine, as you indicated, you have the freedom to get what you need during that first year.
My mother's been told that if you have Medicare, it's actually it to your advantage to rent, without ever buying. I think the reason is that Medicare never pays for a repair, but it'll pay for you to rent forever - so if your machine breaks down, you can get a loaner or a new machine, because the service provided is equipment rental.
May you get your equipment soon, and may your transition be smooth!
- Ridge Runner