Water heater help

[Sage Jankowitz]

So this isn't exactly a rehab question, but not really sure where else to post, hopefully you guys can help.

While I was away in Israel for the past two weeks my family's water heater broke and my mother dealt with the issue herself, since I couldn't be reached while in Israel. She went to a trusted family friend who recommended her plumber who she has used for years.

The water heater needed to be replaced, and the manufacturer told my mother that the model was no longer available, but they would replace it with an upgraded version for $60-$80. She hired the plumber to put in the new water heater, and he agreed to remove the old one for an additional $25. He was here for 30 minutes, installed the new water heater and removed the old one. We just received the bill and it was for $920. Essentially he is charging $800+ or so for 30 minutes of labor.

Now clearly my mother made a huge mistake in NOT ASKING FOR A QUOTE beforehand and I'm really annoyed I wasn't able to handle the situation myself. That being said, $920 seems awfully ridiculous for less than 30 minutes of work for a water heater that was already paid off. We've only be able to connect with the plumber's wife who defended the price and we have yet to hear back from the plumber. What steps can I take to get this absurd charge removed and this guy reported?