Plexiglass alternatives

Hey y'all! Wondering if there are any cheap plexiglass alternatives that are still lightweight? I'm building a soil base for my bird cage so it needs to be strong enough to hold a lot of soil, but still light enough to move the cage around somewhat easily (cage is on wheels, just trying to avoid heavier material like glass). Only three sides of the base need to be clear (or I would prefer them to be clear). The bottom and back panels don't matter as much as long as they're sturdy. All five panels being clear would be a plus, but not necessary :) Thanks in advance! Just trying not to spend $300+ on this if I can avoid it