The United States Postal Service (USPS) simplifies shipping costs by using a tiered system based on groups of countries. The groupings themselves are interesting, primarily because some countries are separated from their regional geographic blocs. There are also a few large countries (spatially) that are not assigned to a group: Western Sahara, South Sudan, and Somalia.

I would assume (perhaps falsely) that the pricing for Priority Mail International deliveries reflect the cost of shipping a package to a given country. Strangely, the lines in the graph cross in some cases, especially at weights below five pounds. It also occurs for heavier packages, though. For example, packages less than 25 pounds are cheaper to ship to Canada than Mexico, but parcels over 25 pounds are cheaper to send to Mexico.

The prices are also only loosely based on distance. The countries excluded from their regional bloc make this particularly complicated. For example, shipping to the UK is significantly more expensive than shipping to Portugal, even though Portugal is geographically closer. The groups themselves are also not based entirely on distance; shipping to the Czech Republic is notably more expensive that sending a package of the same weight to India. I’m guessing there are a lot of factors at play here (frequency of shipping vessels, USPS presence in foreign countries or the cost of contractors, international taxes, etc).

Data sources: https://www.usps.com/ship/priority-mail-international.htm and http://pe.usps.com/text/imm/immpg.htm