I never buy containers. Go to your local restaurant and ask if they have any that they don't need anymore. In my country restaurants buy milk, mayonnaise, ketchup,... in this big containers. You just wash them and voila... They are good for one season because material is not UV protected. Next you can find them at building site. Lime whitewash 25 liters.
Perlite, vermiculite, fertilizer and good soil...that is expensive.