I had two five-ounce pieces of cod. I used them to make four pieces of fish ('n’chips). That means that there are about three pieces of fish for a pound of cod. Considering that fish’n’chips with two pieces of fish sells for about $10 to $14 at a restaurant, it’s a pretty economical meal. 
Not sure if this is behind the paywall, but NY Times had a series on almost famous people. One was H Salt Fish and Chips. Are you old enough to remember that chain? anyhoo, I found the video pretty fascinating: https://www.nytimes.com/2019/08/20/opinion/haddon-salt.html
Sounds about right. Typical restaurant markup is about 3-4 times cost of ingredients. This varies, of course, but that’s a good general ballpark.
Nice video. I think I was dimly aware that H. Salt was a real person. I would not have expected him to still be alive.
I used to love H. Salt Fish & Chips. I know I ate them as a child. In my early-20s in Lancaster, CA we’d have F&C take-out, but I don’t remember if it was H. Salt.
As for Ben Proudfoot, I wonder what this ‘fish & chips connoisseur’ thinks of the ones at Ye Olde King’s Head. I make good fish & chips, but their are my favourite.
King’s Head fish and chips are good, but the best I’ve had locally were at a deli owned by a Korean couple (sadly, the kids didn’t want to carry on the business and it’s gone now). The batter was so light, and the fish was never dry. And the cole slaw was excellent. I miss them so much.