You can do one thing, you can create this table in script itself.
Something like this.
if(Sum(Sales)>=0 and Sum(Sales)<=20,'$0-20K',
if(Sum(Sales)>=21 and Sum(Sales)<=40,'$21-40K',
................) as Bucket.
From Xyz group by Item,Customer;
Now you can create a chart and then count the customers by Bucket.