could this be a solution ?
// Each reward entry is in the follwing format: array_fill(0,WEIGHT,REWARD) where WEIGHT is how frequently you want the REWARD to occur.
$rewards = array_merge(array_fill(0,1,500),
array_fill(0,10,200),
array_fill(0,100,150),
array_fill(0,100,100),
array_fill(0,50,75),
array_fill(0,50,50),
array_fill(0,25,25),
array_fill(0,20,10)
);