Most metal building construction companies will give you a substantial discount on the arena as opposed to a fully finished steel building - they don't have to pour a floor, put a skin on it, do plumbing, windows, doors, etc. and just very minimal wiring for the lights (and a PA system I guess if you want to splurge < g > )
You can do even better if you buy one used.
Hmmmm I'm gonna have to do more research, I was thinking it was going to be some ungodly amount, like $100,000.
I think there are pros and cons to a covered arena versus one that is completely enclosed. My neighbor's arena is only covered and when it storms, the rain blows in and the arena is standing water on the side that the rain blew in. But it's much cooler in summer. I guess it's just personal preference.