Why is getting a breast pump so stressful!

I am so confused and any help would be great! I can’t go through Aeroflow because my insurance doesn’t work with them. I was given a list by my insurance of places to go through. Some places show an “upgrade fee” on the items I want. Others show $0 for the same exact item! But when you go to process the orders at the $0 places there is a thing you sign saying that you understand you will pay the difference if your pump costs more than insurance pays out...but gives you no price yet! How do I know if I’m going to be charged later? Do some places just charge more than others? My insurance covers up to $164 per pump, per pregnancy....