Am I getting ripped off ?

2011 Prius 110,000 miles

Problem started with engine revving/ wanting to stall
Engine light was on , error codes P0101, P0455, P0411
After research on this site I thought purge valve and or spark plugs were the issue
Drove it to and left it at a Toyota dealer to diagnose an Repair.
Toyota mechanic recommended changing purge valve and spark plugs.
Then this message was on my phone
“Update on your Prius...mechanic got the purge valve in and replaced the spark plugs like the tech recommended...vehicle would not restart, hybrid battery showed low so we did a rescue charge but the vehicle still won’t start.......
The vehicle needs a new (used) transaxle and coupler.......
Looking at around $3500 to get back on the road.”

How did it go from driving rough to ~$4000+ to get back on the road?
What does the purge valve and plugs have to do with the transaxle?
This is our 4th Prius and have never had problems this severe so is my good luck up or am I getting taken to the cleaners?