Based on freshwater only, at a temperature of 22˚C, total consumption for a small tank (38L) is about 150kWh (kilowatt hour) a year. A medium tank (114L) 150 - 200 kWh per year and a large aquarium (208L) 200 - 400kWh per year. This is using basic equipment only and merely an average to give you an idea. Exact usage requires an ampmeter, which measures actual energy used and not the energy based on the max output, as some equipment does not run full time (eg heater).
watts/1000 x hours x kWh cost x 30 = 30 days cost of aquarium