There is no usage counter on the page, no “trusted by” line, and no survey of what teams pay. If a number is not from your inputs or from a vendor price page dated on the receipt, it is not on the site.
Rates go stale. The date on the receipt is the day the book was copied. The price page links the vendor docs so you can check before you rely on a total.
Questions about a charge go to the payment checkout once it is open, because that is where the sale exists. The calculator itself does not take payment.