How big, and under what circumstances? Semi-disposable drinking cups are fine for small quantities, but not smart if you are teaching children! You would need something with decent markings for doing dilutions.
I have seen 300ml and up plastic beakers and jugs at a local cash & carry (Smart & Final) intended for group barbecues or professional kitchens. The measuring marks are not up to photographic standard, however. They should stand basic monochrome chemistry. I'm not sure they are significantly cheaper than photographic items.
I keep my eye open at the local camera fairs for useful jugs and measures.