That depends - on the weight of the letter. Take it to your nearest post office to get it weighed, and discover the cost.
98¢
That depends on where you are sending the letter FROM.
3
Postage to Europe from the US is 98 cents for a one-ounce letter.
21p
Domestic postage is $1.39 for an ordinary envelope of uniform thickness.
This depends on where you are mailing the letter from, and the dimensions and weight of the letter.
That will depend on where in the world the letter is being posted from.
44 cents
96 cents.
See: USPO website.
Florida is in the US...