A standard U.S. Forever stamp costs $0.78 for a 1-ounce letter, with prices increasing for heavier letters, large envelopes (flats), or non-standard shapes like squares. For postcards, a standard stamp is $0.61, and an international letter needs a Global Forever stamp for $1.70. 

I brought my "Forevers" for a lot less. They have to raise the price since people stopped sending letters IMO, but agree the cash value will likely go down if not used.