This uses these values for spells by rank (which can be summarized as rank×(rank+1)×0.5), and assumes a single patron divinity for the city-state. Some math corrected, thanks to DrPete.
Starting with a city-state with 60,000 rural families and 1,200 urban families, and 2 divine casters per 9 adventuring classes, the city-state has the following divine casters:
level 1: 3,333 who require no spells per day
level 2: 1,333 who require 1 spell point per day each; total 1,333
level 3: 444 who require 2 spell points per day each; total 888
level 4: 222 who require 5 spell points per day each; total 1,110
level 5: 67 who require 8 spell points per day each; total 536
level 6: 22 who require 24 spell points per day each; total 528
level 7: 8 who require 45 spell points per day each; total 360
level 8: 3 who require 59 spell points per day each; total 177
level 9: 1 who require 80 spell points per day each; total 80
Total 5,012 spell points per day. This assumes that special divine abilities (Turn Undead and similar) cost nothing, or close enough to nothing.
Each rural family produces (per Alex) 1 point of divine energy per week, but the average domain only gets 40% of that (4 per 10 families). Let's start with an idealized domain, however, that gets 100%, and say that differences arise from people who worship other gods than the primary patron.
At 100%, the domain is producing 60,000 spell points per week, or 8,571 spell points per day: enough to power the listed divine casters, plus about half again as many.
Old, Incorrect Conclusion: That doesn't mean it's wrong . . . but it creates the interesting assumption that the gods run their churches on a deficit: they offer the amount of power they offer, because most of it goes unused. If a domain's clerics really started casting, the divinity might . . . run out of juice.
New Conclusion: The gods are doing pretty well for themselves. This also means that the primary divinity of a domain can support more than half of the divine casters in the domain.