You can x area Per unit price and container volume ex factory.
The area volume is around 60~70% container because accessories as like steel skid, flange , bracket , sealing tape box, bolt, external ladder, internal ladder etc.
You can think about around FRP TANK (SECTIONAL PANEL )
The most important is panel quality and reinforcing parts, bolt , kind of steel skid(C-Channel, A-Angle) for your tank.