Prius Issue

I have a 2002 toyota prius. My check engine light and several others (PS, battery symbol and car with exclamation mark.) Have come on. I went to the dealer, and he told me the computer is telling them the electric water pump must be replaced first, and then they need to recheck to see if the Inverter is also bad. The first repair will cost $582, but if the inverter is also bad, I am looking at $3,000. Does this sound correct, or should they be able to determine if the inverter is bad without replacing the water pump first?