Quoted 3k for master cylinder and 2k for inverter!?

Hey prius friends. In the last two months, here's what has happened:

Check engine light comes on, code was read at O'Reillys for potentially coolant inverter/pump system.

Check engine light goes on and off intermittently for 2 weeks

Check engine light comes on along with master warning, vsc, abs, and oil pressure. Turned car off and back on and just CEL was on

Lights continue to go on and off for the next two weeks, only CEL first and then the rest follow.

1 week later, high pitched sound when trying to stop and lost brake pressure but was able to build back up and stop effectively. Car was driven out of necessity for the next week and only happened 2 other times.

So I just brought it to a shop and they guessed the mileage and age without ne even telling them, and said they have one in with the same problem and it's far worse, and it's about $3100 for the master cylinder system replacement and $1800 for the coolant inverter pump. To me that sounds nuts cause the master cylinder from what I researched is only around a few hundred dollars with a few hundred in labor. I'm sure someone else has had or seen this problem. Let me know what yall have encountered or done. Car has 159,600 miles. Lithium battery was replaced at roughly 150,000 and I got the car for $3000 from a family friend.
Thanks for reading.

 

I have already dropped it off at repair shop, so I can't answer that. and I haven't noticed specifically what you mentioned but I have noticed the battery getting hot by the touch, but I don't know what it's supposed to be like normally. I have noticed that the coolant in the lines is warm, and since the coolant has to flow to make warm, and hasn't expanded/leaked from boiling or getting hot, that I'm not sure if it's a real problem or not. Which is why it's been driven until the brakes failed.