Billing is very tricky from the metering to the final PDF bill which includes taxes, promotions and whatnot. So this is hard if you want to put limits on a certain dollar amount. You could also put hard stops on resource usage (say, no more than 500 CPU/hr/month)
Besides, AWS already complicates things way too much by handling VAT like other billable items instead of just adding it at the final step like any sane company would
