I'm not sure about Australia, but here we have restaurant and catering supply stores where you can get deli containers in bulk (25-50 per sleeve) for very cheap. They come in a range of different sizes and thicknesses so you can pick your own. To the best of my knowledge these are exactly what are sold as semi hydro pots online with the addition of the holes drilled out. Although these stores do most of their business wholesale they are open to the public for party supplies and things like that.