Well, your maintenance costs are really these:
electricity...too many variables. depends on total wattage being used x hours per day, and then your price per kilowatt hour. We'll say $20 a month to power the aquarium lights, and heater/pumps/etc.
Salt - buy larger buckets or bags...cheaper this way. a 10% weekly water change puts you at 8-10gallons a week. YOu can get 260gallons worth of salt mix for around $50 usually. So that lasts a while.
water - 20 cents a gallon...so $2.00 a week for new salt water, and probably $1.50 for top-off water
hard to say on the additives...so many to choose from, plus a kalk
bulbs are spendy to replace. and need to be changed annually. $100 a year on bulbs, easily.