Ah, the good ole HSA. The "bringing the power back to the consumers to shop for better and cheaper services" promise. I tried to negotiate with a doctor and dentist earlier this year when I didn't have insurance. I asked if I paid them cash instead of having to have them deal with insurance, would I get a discount? Was told by both that they don't give discounts for cash payments. I tried twice and no go. Not only that, they charged the same full prices that were submitted to the insurance company. Of course, the insurance company lowers that "submitted" price down and pays a certain amount and you pay the rest of the "lowered" price. The doctor and dentist would not even lower the submitted charges down for me direct.
It's a screwed up system.
Of course, many say shop around for another doctor/dentists. Not easy to do when you are in agony from medical issues or have a tooth that needs a root canal.