Which is the extraordinary one, my friend getting handed a massive bill or me getting a small one?

It's very possible he could have haggled it down but why should you need to? Especially in a vulnerable situation like after getting out of cancer treatment.

I can guarantee you I wouldn't have had the wherewithal to fight it in his spot. I barely managed to do anything for 6 months after getting out of my own cancer treatment (and for psychological, not pyshiological reasons).