A higher reward is always possible, in fact a bounty campaign now can set an allocation of $500K per token value for the bounty and this will be distributed after the bounty, however, can they assure that the price will be selling per IEO price? no, because most of the time the value will drop.
You mean that there's an allocation of $500k for the whole bounty but not per token because it might be misunderstood by others and say that each token will cost $500k. I haven't seen a bounty that promised with that amount per token.
But that amount would be the budget itself until the bounty ends.