Crossave searches the same product on 18 eBay marketplaces and Google Shopping in 22 countries and ranks it by the total cost delivered to you: price, shipping, import duty and VAT. It is free.
Duty is calculated with the official rules of the EU, UK, Switzerland, the US, Australia, Canada, Japan and China; where a figure cannot be verified it shows "n/a" instead of an estimate.
To open a search with a link: https://crossave.com/en/?q=product+name