The H stamp is worth 33 cents. Yes, you can add a 1 cent stamp to cover 34 cents worth of postage.
Yes, there is a Elvis Presley 29 cent postage stamp.
20 cents retail. 1 cent as postage.
Unused, you can use it for 14 cents postage.
4 cents.
Stamps are always and forever worth the denomination printed on the stamp. If you need a one-cent stamp to complete postage, and you have a one-cent stamp from 1933 - it is perfectly legal. As to what individual stamps are worth to stamp collectors - that is a completely different question.
$2.00
A 28 cent stamp that is unused can always be used as 28 cents worth of postage. If it is used, it probably has a minimal purchase price of fifteen cents from a dealer.
These are 15-cent stamps -- still good for 15 cents postage.
3-5 cents
.50 cents on eBay
1c 1 cent