Eco - just check with the manufacturers of the bins that the material used is OK for food production -  a lot of the cheaper recycled plastics are great for everything else but as it cannot be verified that there are no potential problems with the source plastic (such as chemicals that it may contain or have been stored in it) you have to make up your own mind on whether you want to use it or not.

In terms of the Hydroton (expanded clay): I do not feel the benefits justify the price of a whole bed full of the stuff.  It is easy on the hands and do weigh less than gravel, but at most, I will consider a bed that is topped off with the stuff, but not filled completely.

I have started a group for South African AP members to share concepts, sources of materials etc.  Please have a look and join if you think it will help.