There are a lot of concerns about the gold conversion rates in this story. Not gonna lie, I just estimated a rough figure for the sake of saving time, but a lot of people are commenting about it, so I decided to actually do the math. I am not good at math, so I may be wrong here. (information source is the web of course)
1) Gold price as of 1991(Nov) : £6572 / 1 Kg Gold
2) 1 Galleon is £4.93
3) The Price of 180 Kg of gold in pounds will be 6572.58 x 180= £1183064.4
If, converted to galleons 1183064.4/ 4.93= 239972 Galleons.
This is 180Kg gold =239972 Galleons
But the MC did not convert all the gold into galleons. In the chapter, He only kept around 50,000 Galleons in the Gringotts. It was just an estimate, but now, I will be changing it in the story to 140,000 Galleons.
Also, the broker's share was 12% of 180 Kg gold, which is 21.6Kg of gold. That makes his cut around £141967 or 28796 Galleons.
I know it is overpriced, but the MC only has one connection for exchanging gold as he is new here. His other option was the Gringotts, which had a commission rate of 20%.
Have a good day-