Hello, my friends！
As far as I know, there is only the most recent tariff content on the Internet, and I also know that postage is variable. As an outsider, I would like to know the changes in postage in the United States and Canada in the last 30 years. Such as the cost of international air letters, domestic letters, how much does it take to register. Depending on purchasing power, you can write down the exact amount first, and then write down the conversion unit of 500ml cola purchased locally.
And thank you for your answers! 
Check out this Wikipedia article and see if it covers what you need:
Hope that helps!
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Very helpful indeed!