It varies massively depending on what grade you want to make it, mainly the cost in polycarb. No idea how much the Robo Challenge arena cost but definitely a five figure sum I'd imagine. Size-wise it's 4.8m x 3.6m; the smallest arena featherweights play in at the moment but that's considering that the other events host feather fights in their HW arenas.

I made one for our Scot-Bots venture a few years ago, also 4.8m x 3.6m max but modular so we could bolt and unbolt walls to get different size configurations. Nothing fancy, just the walls and some wooden loft flooring boards for the floor. There was also some warping when welding the walls so it's a bit skewy in places, but it does what it was designed for. Can't remember the cost, but the polycarb was free, reclaimed from a bus stop refurbishment company, the steel was quite cheap from a local stockist and the flooring was from B&Q

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