where i live, there are a certain amount of kilowatts per month that you can consume before you start paying a premium
so after a certain point, it becomes less cost-to-output wise to keep adding wattage
you really gotta look up your city's power rates, premiums, on-and-off-peak hours, etc
it's some complex math in some cases to figure out how much shit will cost per month and at certain points in the year
but if i had to guess... 80-100 extra dollars per month during veg sounds about right for 2k watts
i pay about 25-45 extra per month - depending on the season and growth stage - for a 900 total watt grow
don't forget, fans can run over 100 watts