[pharrington]

Assuming IE11 users are otherwise representative of the customer base, multiply your total web based revenue by 7.6%. (If this assumption is wrong, then just check your reports to get the correct number.) If, for example, the business in question makes $10M yearly revenue, your estimate has 7 entire devs working exclusively on IE11 support fulltime, year round.

That is one fancy as fuck ecommerce site to be that reliant on features in modern browsers that lack automated transcompilation/shim generating tooling.