Overpirced CPAP machine

Dynamic Health Care Services billed BC/BS over $1200.00 for a CPAP machine that sells for under $500.00 at Walmart. Since I have not met my deductible I have to pay over $600.00 out of pocket.  Why isn't Walmart on the list of CPAP providers since the cost are substantially lower? I understand there would be NO agreement between the two parties but in this case it is not needed. Can someone explain why BC/BS allows this to happen and when will it be fixed in an effort to lower our medical costs? Is BC/BS interested in lowering OUR costs wherever and whenever possible?