If you're on a budget, see if you can find any bus stop refurbishing/repair companies near you. They may be able to supply you with used 5mm polycarb panels, though obviously the quality of them can vary. Got a large supply of these from another roboteer a few years ago who knew a neighbouring company, gave us plenty for a small-walled featherweight arena, and the panels would be an ideal size for a beetleweight scale arena.