MK7, I have no personal knowledge on the cost of replacing the Prius high voltage battery, but did look online and found the same information on costs to do it.
There appear to be places where you can have bad cells replaced and the cell voltage balanced (important) before you install it. Another appears to swap out the packs. Of course you can buy a new pack.
I bought my Prius in MA, that had adopted the CA standards and it increases the warrantee on the high voltage battery from 100K miles to 150K miles.
I bought my Prius 4 years old with 8K miles. I currently have 44K miles so I have a long way to go before I have to think of the high voltage battery. There are many on the Prius forums that have not had any battery problems to 200K miles. I thought about the potential issue but it soon became a big issue to me to concern myself with.
Brent