I'm not sure that's possible. You know the arena score doesn't accumulate, right? It only counts your highest score from a single win streak. The most you can get mathematically is about 5,000~6,000, if you play all advanced battles, have all level 40+10 5* units with high stats (the +10 would mean you pulled that unit at 5* 11 times and merged them all together - 10 is the most times you can merge a unit), have one of the bonus units, and win all your matches without losing any units. Basically, you're only getting a really high score if you're sinking piles of real money into the game.