It costs more than you think, it is usually a 3GPM faucet head that is used to feed a 50’ Diameter circle, at the current reclaimed (read cheaper) water price of $0.00401 per gallon for the first 3,000 Gallons and $0.00414 per gallon after that, assuming a 60 x 120 plot you would need about 6 sprinklers, taking that into account you are suppose to leave it on for 20 min, so 6 sprinklers x 3 GPM x 20 min= 360 gallons per day, watering every day for a month will give you 10,800, now that will be 3000 gals at $0.00401, or $12.03, and an additional 7,800 gal at $0.00414 per gal, or $32.29 a month, that is $44.32, now times 12 months that is $531.84 per year just to water your lawn
EDIT: that took way to long to actually do, and I now realize that I probable should have been doing real work