Well that would depend on what the hieght of the tank is,
If the tank is 72x24x24=180gallons
72x24x30=around a 220gallon, This is a guess. The 72in long x 24inch front to back come in several different depths. 18,22,24.30, and then there are you custom tanks sizes.
As far as worth, a used tank is only worth about $1-$2 a gallon. It is only if you have the stand, canopy, and other equipment that you might be able to make any money. And even then, it depends on how nice and clean everything is.