Open Question: can they really charge me this much for a nebulizer?

i took my son to the pediatrician about a month ago. he already uses inhalers for allergy induced asthma. they said he needed something stronger. a nebulizer. i said ok do i just get one at the pharmacy or do i call my insurance. she (nurse) said no we will give you one here and the billing/insurance people will be in in just a few minutes to get you setup. i asked but how much will this cost me and she said nothing your insurance will pay for it. then the billing/insurance lady comes in with a nebulizer and papers. i asked her do i return this when im done and she said no its yours to keep. i said and this doesnt cost me anything and she said no your insurance co pays for it. ok. now today i get explanation of benefits from my insurance saying it was out of network and i owe the medical supply company $419.99. i called the insurance they said not their problem i have to deal with the pediatrician and medical supply people not the insurance. of course the medical supply is voicemail only. the billing people from pediatrician are gone for the day. how is this possible?? this same nebulizer sells for $42.90-60.00 online and in other pharmacies. who would i need to call to fight this the pediatrician or the medical supply people?? my son only used the nebulizer for 3 days then the pediatrician said stop using it and go back to inhalers, i didnt even open the 2nd set of tubing they gave me... what can i do about this? i cant afford to pay $419.99!!