How do I dispute a hospital charge that was not clear when I requested an estimate for a procedure?

I was told that steroid injections in my back could be expensive, so I put them off for a while. Then the pain got to be too much, so I used the website tools to "Estimate your cost for common procedures and treatments." It took me to https://my.providerfinderonline.com and the dr I had scheduled came right up and the estimated cost was approximately $80. I could afford that, so I went ahead with the appointment.  A few months later I received two bills - one for $71 from my Dr (as expected)...and a $750 bill from the Hospital (unexpected).  NOWHERE in the online information or through the dr's office itself was there any hint that there would be an additional hospital charge.

Why on earth - if you're providing a cost estimator tool wouldn't you make sure your members knew about the overwhelmingly most important charges they may incur that are associated with a procedure?

Not only can I not afford to pay $750 for that visit, it has made the entire process worthless, because the recommendation from this dr was multiple series of injections.  Therefore, the one series I did have was pointless and a waste of even the $70.

Please tell me the best course of action to dispute this charge.

Thanks!