I was meticulously recording egg statistics (among other things) for our hens every day.
On average our plymouth rocks laid 221 eggs per hen per year. That works out to an average of just over 4 eggs per hen per week.
This average over the year includes each hen moulting twice (they do not lay through a moult), some hens going off the lay as they were injured, each hen going broody and not laying an average of 0.3 times each (they were not allowed to hatch so stopped being broody after 2 weeks or so).
Average number of eggs per hen per month:
These hens were free ranged through the orchard and not provided any extra light or heat. They foraged for between a third and two thirds of their diet depending on the season. Feed costs should be very low on acreage as they can forage for most of their feed.
We had one hen who lays a different looking egg, she laid far more than the others, her eggs were not counted so that we have a more accurate average number of eggs for my old strain of plymouth rocks. I also did not include eggs that were laid while we were away as they were collected by our neighbours and I did not want to impose that they also count eggs as well as feed and water them.