There was a discussion last year of concern over long dishwasher cycles using excessive amounts of energy. I posted some figures on my DishDrawer's power consumption. The figures were quite low, seems to me.
Scenario 1: Household water heater on 70°F to insure the dishwasher must do all the heating. Normal cycle, 115 mins, 5 water changes, 140°F main wash, 150°F final rinse. Power consumption, a tad less than 0.6 KWH. Figured at $0.15/KWH, that's 9 cents.
Scenario 2: Normal Eco cycle, 88 mins, 4 water changes, 125°F main wash and final rinse. 0.4 KWH. 6 cents.
Scenario 3: Heavy cycle, 132 mins, 7 water changes, 150°F main wash, 163°F final rinse. 0.68 KWH used. About 10 cents.
Fill is about 45 watts (pump runs at low speed). Water heating with recirculation, maximum 650 watts. Pump recirculating, varies about 75 to 110 watts. Pump drain, 30 to 45 watts. Drying fan, 7 watts.