Tank and stand, = 200ish
rock = maybe 300
sand = toss it, buy new
The rest has no brands, condition, etc.
I've seen people's "amazing corols", generally garbage unless it's exactly what you were going to buy anyway. I would guess if he can't spell coral, he can't take great care of them
Maybe worth a few hundred. Maybe.
If you want all the fish, worth maybe another 400 (assuming good size, condition, etc)
So depending on what the gear is, it maybe be worth upwards of 2200, maybe more if it's exactly what you're looking for. If you're interested, and it's clean and in nice shape, offer 1800 and work from there.