Prices are wildly varied depending on the tank mfr, stand construction, included equipment, age of tank and most importantly, who is selling it.
i.e., the guy who set up a beautiful custom 180, brand new, 5 years ago and is now taking down because he is moving/etc will want (and likely get) more for his tank than someone who picked up a tank as a hand-me-down or garage sale and decided they just didn't want to get into it.