(((Mera)))! Sometimes it helps me to let go of anger like that by thinking through something like the following: what happens if you don't "win"? Ok, you will be out a good deal of money and that's very painful. But, weigh the cost of your stress levels in order to hopefully get it back. I'm not saying to drop it but it may help to get it mentally in perspective.
I've been in situations where I've felt powerless and then get angry and then I want to drink. I think that part of my work in becoming and staying sober has been learning to choose my battles and look at them differently. I may still choose to fight but I don't feel as helpless if I realize it's a choice.
For me, feeling helpless is the worst possible place to be.