As far as I know bustadice pays the highest maximum reward on a single bet followed by primedice and Betcoin and lot others but its literally impossible to high the maximum outcome unless you are enough luck to win the lottery. 
How much is the max profit per bet on bustadice? I do not know about it so let me know if you know about.
At the moment, the biggest bet someone could make is about ₿ 4,357 at 1.01x. The wager size is only limited by the maximum profit, so the exact number changes all the time.
Source: https://bustadice.com/faq
I don't know if it's the highest max bet amount on a single bet but I guarantee that bustadice surely have an insane bankroll for offering this huge margin.
