If you go for a big tank, something in the reach of 90g+, the cost to fill the tank up with plants, CO2, filtration, and substrates can go up really quick.
I think my initial cost of my high tech 40g, minus plants and fish, is about
$700 (tank, CO2, substrates, lighting, filters, ferts, and other stuff). I have about 40 fish in my tank and they aren't even rare or exotic. They are about $120. Plants? $200 of plants and not counting those that didn't make it.