The cost of an arena varies massively, from the top end of Creative works to a DIY approach. An effective design will create a stimulating environment that players connect with, which leads them to want to come back again and again and tell their friends how much fun they had at your arena.  For a 300m2 Arena, Creative works are around $90,000 inclusive of structural walls built by a third party, down to 30,000 for a DIY build at a reasonable quality.