it all depends on what you do with the tank... fish only, fish only with live rock, corals and they types of corals ect... there are somany varriables that unless we have a general idea of what your gonna do with the tank and your stocking levels and your planned maint. schedgle there is no way to give a ball park estimate it could only be 50 bucks for salt once a year if you only have to change a few gallons a week with a one small fish bio laod.. but it could be 50 bucks every 2 weeks for salt if you have to change multiple larger amounts of water with a heavy bio load.
some corals require additions of chemicals/trace elements where others dont, some require micro foods where some dont.. some require water that is so clean and sterile and some like dirtyier water so it could be 50 bucks a month maint or 500 bucks a week for maint just depending on what you do with the tank..sorry i was no help