Midas review: Diagnostic and o2 sensor charges

I recently had a diagnostic done for a clanking noise in my engine of my 03 GMC Sierra. It is $99 for diagnostic charge. I ok’d them to check out a few parts possibly to fix the issue and replace the O2 sensor. I was quoted over $1500 to replace engine parts. I did not want to move further with that option. I picked up the vehicle and was charged $226 for a the O2 sensor when the part price is regularly $75 for that part number. There were no number of hrs listed for labor charges which came to be over $400. With taxes the bill was $790 and I still have the clanking noise to deal with. When I checked under hood later, there was a hose disconnected from the engine block. Pic below