Also, each arena should be different.
Solitude would be similar to the Imperial City's arena. However, Markath's might be assymmetrical craggy rocks and crevices. Whiterun might have frozen ponds that reduce balance and are easier to be staggered on, with pillars of ice acting as obstacles. Another might be foresty, with trees and platforms amongst them, for an arial acrobatical event. And one might be ringed in lava, with hot damaging geysers firing off periodically. That way, you would always have a reason to visit the other arenas even if they don't pay as much.
Also, each arena should offer different fights. Solitude would always offer playable races to fight, but the other arenas once you beat their associated questline would have creature fights. The creatures that you fight would depend on the area in which the arena is located, e.g. fighting snow trolls in Whiterun, wolves in te foresty one.