Airless Tires
https://www.youtube.com/watch?v=HB4fOyXox4E&t=213s
I bet you've seen some of that videos with tubeless/airless tyre demonstration. How about to build one with your hands ? Cheap and simple, Using onle pvc pipes, bolts nut ands to fit all together. This construction still needs to be modified. But in general, it's a fully working concept.
Amazing...