Complete custom built 180 gal. setup.

[Aquattro]

Al, you listed a lot of stuff without details. For example, what type of lighting? (Brand, watages, # of bulbs, etc.) What make and model of filters, skimmers, etc.
You may even find you can get closer to your price by separating the parts.
An example of some used prices...I bought 140 pounds of rock, 200 pounds of sand, 7 fish, 50 hermits, 30 snails and various shrimp,stars, etc. for $400.
I bought a dual 400w/10k MH setup for $300.

These prices are a big drop from their new price. Unfortunately recovering money spent when selling your tank is difficult. Especially when it's a tank like yours. Not many people are in the market for a 180g tank setup. This makes offers fewer than you'd like. The end result is that your stuff is only worth what those few would be buyers are willing to pay. And we're generally cheap :D
Seriously though...if your in a rush to sell it, you need to cut a lot off the price. If you can wait an extended time, hold out until the "right" buyer comes along.
Good luck!