I'm sure you recognize the same dynamics we have in our small flock - we had 7 birds, then later went up to 10. There is a down time for the molt, and production is slower in the winter. These birds are now essentially three year olds, so I expect there to be a drop in production. Yet all that said - we're still conservatively averaging 3 eggs a day. So you extrapolate out an average of 100 eggs / mo (again - even that is really conservative) and $50/mo on feed/supplies (and let's be real - that's generous, it's probably more like $30/mo typically) and the numbers play really well for backyard chickens.

That said - we have had a lot more coop expenses than expected, because our neighbors wanted to be jerks about it and I wanted to keep the peace. So realistically the "savings" we would have had in egg costs have likely been eaten up or significantly reduced by having to rebuild / move our coop.