I completely sympathize with your situation, and prayers are being said.
We are in the same boat. The finances to support any more children are just not there. I am also just learning NFP (Billings Method).
I have 2 friends who have used NFP for years and it has worked perfectly – they get pregnant when they want and don’t when they don’t. I figure if they can make it work, so can I. The method is actually fairly simple when someone explains it to you.
It is hard to have faith when life gets difficult but I try to remind myself that God knows my struggles and he would not send a child that we truly could not care for.
I’ll be praying for you,