budget for my 125 and a quick breakdown.
filter kit for RODI
unit- $25 (replace once a year)
600g of salt mix (20% bi-weekly)- $170
2 new 96w PC
bulbs- roughly $80
2 new 24in T5 bulbs for refugium- $40
food (hard to calculate)- prob $100
so all in all, im looking at roughly $415 per year for my 125, that's not including the extra electricity, water consumption and minor odds and ends (meds if needed, sponges for cleaning, etc). now granted I run a fairly simple setup, I don't have any reactors or excess equipment running, so my cost is a bit lower than most, but still, not even close to thousands of dollars a year.
now the money ive setup on the tank itself (new equipment, new fish, etc) im prob somewhere between 4-5g so far since I bought this tank, however it is a 125 and I tend to ignore pricing when it comes to fish.
also id just like to say that once it graduates to an obsession (which it will, don't worry) money isn't even a factor that you'll be concerned with. instead of "wow I spent how much money already?!?" youll be saying "how can I free up more money to spend??"