2010 Toyota Prius - Heat shield costs adding up

I took my Prius 2010 to the shop for an oil change and they said that I need to replace the heat shield. They said if I brought it sooner, they were able to fix it but now they have to replace and it costs about $450. Then also they fixed the heat shield about an year and half a go and they charged me for $230. When I asked why it is damaged again, they said that was a different heat shield.
So my question is that, how many heat shields my car have and does it really cost that much to fix or replace?
Thank you

The next time this happens go to an independent muffler shop for a second opinion . It also might be cheaper . As for cost I doubt if anyone can say if it was fair or not without seeing where the heat shield was or how much labor was involved .