The cost is $0.70 cents to send a postcard to the US. As a note, if I want to send one to Bermuda from the US, it is $1.20.
If I would like to do the same from Hungary either to the USA, or to Bermuda, then it is 735 Hungarian Forint (HUF), which is currently $1.81 USD, because $1 USD is currently 404.99 Hungarian Forint (HUF). The value of our currency against the USD is record low nowadays.