$300 seems low to me as well, but the order of magnitude spread isn't suprising at all. About 5 years ago I went into the ER in NYC due to extreme dehydration. They gave me some saline and sent me home a few hours later. Later I got a bill for $250 which was above my ER $150 copay so I called them up and it turned out they didn't realize I had insurance. A month later I got a "fixed" bill for $3000 to my insurance of which $150 was my responsibility.

My example of a magical 12x increase given single exact same procedure coded identically, means I find a price increase of ~43x from $300 to $13,000 between different hospitals quite believable.