I don't remember what it cost to set up my tank because I did it in 1971, but I know it was practically free.
I did buy the tank but besides that, I collected the water in the sea for free. I collected the rocks for free on my many trips to the tropics. I just put them on my lap on the plane. Now that is illegal and if you bring it on the plane, they will shoot you.
Over the years I traded or gave away all those rocks and built most of the rock I have now as it looks better and is hollow. Also practically free.
I built all my lighting systems out of used equipment of which I have had 7 or 8 over the years. Now I have a water cooled LED system which cost about $25.00
I also built my 5' skimmer for probably $8.00 and got the 2 pumps for it very cheap when LFSs went out of business.
My first Ozonizer I built but it tended to dim the lights in the neighborhood so someone getting out of the hobby sold me one very cheap. I have had 4 or 5 of those so far.
I built the stand for free and many of the fish I get from stores that are covered in parasites and receiving last rites so I got them for free or almost free and I cured them.
Corals I pay for but they tend to grow. My tank has 8 or 9 vintage bottles in it that I collected while SCUBA diving in New York.
If I had to put a cost factor on my tank now it would be about $100.00 not counting the tank itself and livestock.
I have no quarantine or hospital tank, no controllers, no medications, no reactors, additives, pellets, Rowaphos, GAC etc. Just water.