Good to hear some decent experiences.
I am not on medicare but on a PPO provided by my employer. My personal experience with the cost and how it is controlled is poor. Actually, it is probably a good illustration of what is wrong with the non-single payer system here in the USA.
I have good comparison material: I had 3 times the same hernia repair surgery, but each time at a different hospital. Each time I spent about 4 hours in the hospital, of which ~1 hour in the operating room under full anesthesia. There were no complications, so the hospital effort should be similar each time.
The negotiated amount the hospitals charged varied wildly: from $8,000 (Good Samaritan San Jose), $17,000 (Stanford) to a whopping $25,000 (Fremont surgery center). This excludes the fees for the surgeon and the anesthesiologist.
So: a factor 3 difference in hospital costs for the same thing! Hernia repair costs between $1000 and $2000 in most European countries, by the way.
Since this was non-emergency surgery I had the option to 'shop around' for the hospital. And since past experience wasn't too die for I picked a different one each time. The problem was: no hospital would tell me up front what they would charge, not even remotely. So there was no way for me to trade off cost vs quality.
The expensive $25K hospital was out-of-network. They only told me that I would pay less out-of-pocket than the in-network hospital (Stanford). That was true, but my employer (who is self-insured via United Healthcare) forked over the rest of the money. I had no incentive to stay in-network, nor did I have any indication that they would scam us so bigly.
I was able to negotiate my out-of-pocket part of the $25K bill down from $3K to $1K by explaining that they charged 3x the amount that the previous hospital did, and that the out-of-pocket co-pay limits are rather nebulous with so many charges. I tried to make the case that my bill should be $0 as I brought them a very lucrative business at my employer's expense. That did not work, but I thought that I should be entitled to a larger part of the 'action'. If doctors and hospitals conspire to extract money from insurances, why can't patients?
I tried to bring this scam under the attention with my employer and the insurance company that handles the claims for my employer. Nobody seemed to care, even though they just got ripped off by serious amounts of money.
Healthcare and capitalism simply don't go together well. Good information is needed for capitalism to do 'its thing'. It needs realistic options to walk away from if needed. But when you are sick you are not in the position to comparison shop and negotiate. And even in non-emergency cases, hospitals bend over backwards to not give any meaningful cost information beforehand. After the fact they send an astronomical bill (which is hard to comprehend and check), which then get 'negotiated' to about 1/3 by the insurance. As a result the USA pays 2x more for healthcare per capita as other western countries for less coverage. The system is rigged.