Blue Cross tried to make me pay double for a CPAP machine?

I was recently diagnosed with sleep apnea and my doctor connected me with a medical supplier to get fitted. After setting an appointment I was told to call a third party (CareCentrix) to discuss the financial arrangements and provide them with the billing codes for an estimate.

I get CareCentrix on the phone and after I give them all the codes, I'm told that Blue Cross has a 10-month "rental requirement" for compliance purposes. The cost will be over $900 for the first three months to cover the machine and supplies, then an additional $125/month for 7 months. Bringing the total cost of the machine to over $1700!

This seemed way too high to me, but it was just prior to my appointment when I got this information, so I went anyway. The technician was nice and helped me through the fitting process, but I was texting my mom in between and she found the CPAP machine online brand new for just $600. WTF. I finally stopped the technician and said the insurance company was trying to charge $1700 for the machine, and asked what it would be for me to just pay out of pocket. He stepped out of the room for a minute, came back and said the cost would be $850 for the machine and 3 months of supplies if I just paid out of pocket. So half of what the insurance company was trying to charge! I told him I wasn't taking the machine today until I sorted out the insurance issue but that I might come back.

Needless to say I am angry and confused. I thought using insurance was supposed to be cheaper, but it seems like they just tried to rip me off? Also I'm slightly concerned because when I scheduled the appointment the person said I was required to have a credit card on file, so I gave them my HSA debit card number. I'm worried they might try to hit me with some bullshit charge or bill since I went to the appointment and didn't take the machine.