Our Agway sells both metal barrels with/without removeable lids, (which we use for burn barrels) and, for the purpose of this thread, heavy-duty 55 gal. plastic drums for $35 or so, similar to what Emergency Essentials sells currently for $75 plus shipping. The drums have been used to ship food grade syrups and juice concentrates. The drums have been labeled as being used for such.

I think these could be cleaned satisfactorily by letting some dish detergent solution sit in it overnight and then multiple rinses.

Other sources of these drums might be college/university warehouses or kitchens, university salvage warehouses, soft drink or other such bottling plants or distributors, other food packaging plants that use barrels of liquids/syrups in their product,etc. I'd avoid re-use of the drums in which floor stripper, waxes, insecticides, and other -cides are shipped.