Before getting started you need about 6000 gold. Go to the Imperial City Market distict. Then head into the staff shop.
Purchase the staff of Apothesis. Now use your Duplication cheat and Duplicate some soul gems. I would suggest Lesser Soul Gems or greater.
Now head into the Arena Bloodworks. With this weapon you can usually kill your oponents with One shot (some of them are more like the Current Grand champion).
As soon as you kill your opponent run down collect your reward and then head back up and kill some more.
Do this over and over. I complete the arena in less then One Cyrodil Day.