Nutz wrote:

Sure its not metal but it's not politics or global warming!

I was wondering why rotomolded plastic water tanks are so expensive.

The raw materials are generally regarded as cheap, the manufacturing process
seems on the surface to be simple. I guess transport / distribution of a
bulky product could be costly. Anyone got some ideas?

What everyone else said about time and labor costs.

The interesting thing to note is that unlike injection or blow molding,
roto-molding does have some home shop DIY potential since the mold
doesn't have to be super strong (like injection molding), doesn't
requite complex support systems (like blow molding), and doesn't even
require a big oven if you install heaters on the mold itself and so some
simple slip rings to get the power to them.