Here's the most important thing to remember:
DME (durable medical equipment) suppliers are in it to make money. (Like any business!) And there are good ones and bad ones. If your insurance is paying for the machine, even in part, they may steer you toward a less expensive one because they get the same benefit from your insurance company no matter which one you buy. So shop wisely. If necessary, your dh's doctor can adjust his prescription to state that you must have an 'auto' machine, that it must have a heated humidifier, etc. And keep in mind that masks don't 'come' with machines. Both are separate. Any mask (of any manufacturer) can be used with any machine.
I'd strongly suggest reading and posting on one of the sleep apnea forums like cpaptalk.com or apneasupport.org and also as a pp said, find out what your insurance coverage is and if your carrier has a list of providers that you must use.
Oh, and about the masks. He will have tried one with his sleep study. If that worked well, great. If it didn't the boards will be a good place to get an idea of other masks to try out. There are nasal masks, nasal pillows, full face masks, minimal full face masks, hybrid masks...a whole array. You can see almost all of the masks online.
Good luck!