Why are birthing centers so expensive?

I'm looking into birthing center options but my goodness they are expensive. Considering my insurance won't pay, its so much more to go the BC option. I've called so many in my area and they range from 4k-6k and I've only found one option under 5k for a CPM not a CNM.  Some will offer a self pay discount of 10% if paid by the first visit.  I'm not made out of money, so dropping this kind of cash in less than a years time isn't easy.