[EricH]

Originally Posted by Akash Rastogi

....traffic cones

Guess I should say, that there are 4 of those in my family's garage right now (obtained for use with soccer--goal posts). I'd guess they weigh about 8-10# each, but they're plenty tough. (I think one of them has a minor crack, but that's it.) Barring sharp robot parts, you'd probably only need 2-3 spares per event--and if you needed more, you'd just have to find the nearest store that sells them.