I don't know how much it can cost. But you can use Google analytics with its geo reports and ecommerce tracking. That will give you a clue on the countries of the buyers.
You can't get this reporting in Magento. I recommend you use an extension for this. The extension would be able to tell you this.
Some extensions are a one off fee or a monthly fee generally starting at $50USD.
If you want a suggested list then let me know.
We provide magento customize service. If you want to make this feature for your website, you can contact us on the link: http://www.magewoo.com/magento-services.html or send email via firstname.lastname@example.org.
Hope it's helpful for you.