As a mother who breast feed 2 babies for 18 months each. I would purchase breast milk. If I was not able to nurse... and my child was a premie or ill I would do anything in my power to make sure they had the best.
Also I would like to add, I donated my over supply of milk to the north american milk bank... that was one of my most rewarding days... donating something I truly worked very hard to make :)