Get this though: if you have insurance and your insurance doesn't cover something, you often
can't negotiate. I had a $10,000 procedure that insurance didn't cover (i.e., I hadn't met my high deductible yet), and I had no choice but to pay the insurance's agreed-upon rate (which I feel was higher than what I should have been paying out of pocket).
So it was kind of negotiated, but through insurance and their negotiated rates not an individual's out of pocket negotiated rates.
This was also a service where I wasn't informed that a second doctor was out of network, which also screwed me me (and there's literally nothing I can do about this after the fact).