disagree here, if you setup the tank right it wont cost much to run. my 550 G costs under 15$ a month to run. Food yes it will cost a lot for big tanks.
Dang, teach me your secret? Do you have solar panels? What type of pump are you running?
Assuming what appears to be the Australian national average of $0.248 per KWHr (or $0.25 per KWHr in US Dollars) you run your 550G tank on less than 2 killowatt hours per day? That's the equivalent of running an 85 watt pump 24/7.
Add lights, heaters, air pumps and potentially additional powerheads and that will put you way over $15 per month.
How do you pull that off?
Edit:
My 770G uses the following (at $0.34 per KWHr- PG&E rates that the OP would also be charged):
Laguna Max Flo 4200- 160 watts costs me $39 per month
1,800 watts of heaters - in the winter they are on about 4 or 5 hours per day so it costs me ~$80 per month to maintain 78F
Air Pump 16 watts - $4
132 watt flourescent lights- I only turn them on when I'm in the fish room, since I have a skylight, but if I ran them for 8 hours per day like most people, that's $11.
Monthly average total cost to run my tank is around $70 since in the summer I don't have to run heaters.
If we are talking about a tank large enough for an arapaima, multiply everything by at least 10 to get your monthly costs.
PS- Pacumom is also my idol!