I'll be looking for one too.
Depends on if its AGA or Acrylic. If its glass, i wouldnt pay more than $1 per gallon if its used.
If its Acrylic, it will be worth more used. So I would expect to pay more like $300.
Thats for the tanks only.
But on this site and craigslist, lots of people unload complete setups for dirt cheap. Sometimes for the price of what it could go for tank only.
So just keep your eyes open and look for deals on here and craigslist.
But if you want new. Then expect to shell out some extra.