Toyota Repair: Power Brake Booster, power brake booster, regenerative braking system

Question
I have a 2003 Prius and I was told that the power brake booster had a leak and it was going to cost about $1500 to repair.  What is that and why is it so expensive?  People I have talked to say it is a crazy amount to pay for that kind of repair.  I would hate to think that I am being given some incorrect info because I am clueless about cars.  

Answer
It depends on what, in particular they're talking about. The Prius is equipped with a normal vacuum assist, and the electronic regenerative braking system.

Go to an indy mechanic & have them look at it. You can always try a used part off a wrecked Prius too.