The price of one US postage stamp sufficient to mail a one ounce letter to any destination within the US is $0.44. That price is likely to increase soon.
Note also that there are a great variety of US postage stamps available for various purposes. You can buy a single stamp with a value of $0.01, but you can also but a single stamp with a value of $7.80, $10.00, even more.
First class postage was 3 cents for the first ounce in 1940. A post card cost 1 cent.
The first ounce is 1 Forever Stamp (currently 47 cents) additional ounces are 21 cents. Postcards are 34 cents.
Actually, the 1 cent postage on postcards was from July 1, 1898 to Jan. 1, 1952. I have a post card in my possession with a 1 cent stamp on it that was dated Oct. 24, 1934.
For a standard shape envelope and not more than 1 ounce the postage is 75 cents. You can buy a 75 cents stamp at the post office. You could use two 44-centers of course, but you would be over-paying.
The cost of an ounce of First Class US postage in 1910 was 2 cents. That rate went into effect in 1893 . It stayed at that price until it took a temporary jump to 3 cents during World War 1.
The price is 98 cents to mail an ordinary 1-ounce letter .
The price of a US postage stamp has gone up to 45 cents in 2012. This price is for a regular letter with a weight of 1 ounce. If your envelope is overweight, there will be an additional charge of 20 cents for each additional ounce. There is no discount to purchase a book of stamps.
The price of a US First Class Stamp in 1857 was 5 cents. It was good for one ounce of First Class Postage. It went down to 3 cents per 1/2 ounce in 1863.
The cost of the first postage stamp (Scott #1) in 1847, was 5 cents.
The Stamp Market Quarterly lists the 1-cent blue with "Z grill" (Scott Catalog # 85A) at US $2.9 million. There are only two known. The price above is for a used stamp in Extremely Fine condition.
The H stamp is worth 33 cents in postage. The US has never de-valued their postage stamps. In the US, they are still valid for postage at their face value.
Whatever the first class postage is. Today it is 49 cents
In 1934 the price of a first class stamp was 3 cents. A postcard cost 1 cent.
US postage for first class letter was 3-cents.
The cost of a First Class US postage stamp in 1903 was 2 cents. It was set at this rate in July of 1885. It stayed at that price until November 1917.
The cost of a First Class US postage stamp in 1891 was 2 cents. It was lowered from 2 cents for half an ounce in July of 1885. It stayed at that price until the temporary raise in November of 1917.
You can use US postage since origin US but since int'l will take more than 1 stamp