Four cents if you use it for postage. The value to a collector will depend on what stamp it is and what its condition is. You can consult a stamp catalog to find the information that will tell you if it has any value. Chances are if there is nothing special about it it is worth just a few cents.
Need more information on the post card to determine the identity. Consult a postage stamp catalog, usually available at your local library for exact identification and catalog values.
20 cents used; 50 cents unused
yas
yes
4 cents. Put it on your next letter.
An unused 3 cent stamp can be used for postage at 3 cents. Used these are mostly of minimal value, not likely to be purchased by a dealer in small quantities and can be purchased for about 15 cents. Mint will vary depending upon the actual stamp, but most can be purchased for under 50 cents. You would have to use a stamp catalog to identify the stamp for the specific value. And purchase price is 3 to 4 times what a dealer would pay for a stamp.
All U.S. stamps since the Civil War can still be used to mail letters and packages. So a 4 cent stamp is worth 4 cents today. If the stamp is old you can check in the catalogs to determine collector value. Few stamps issued since 1950 have significant collector value.
on e-bay they are going for 3 to 7 dollars
$0.85 mint, $0.25 used
If uncancelled and used as postage it is worth (surprise) 4 cents.As a collectible stamp its value will depend entirely on condition, which must be determined by direct observation by an expert in stamps.
This a common US commemorative stamp. Its retail value in good condition - no missing perforations or thin spots and full gum if unused and lightly canceled if used is from 10 to 20 cents retail. Wholesale, the value is 50 cents to 75 cents in lots of 100 for used stamps Unused about 65% of face if you have enough unused stamps to make it worth a dealer's time. Full sheets and plate number blocks can often be sold for full face and maybe 20% more.
In good condition they would have a value of about 15 cents. That means that it is the cost of cataloging and storing the stamp and a dealer would not be interested in buying it. Consult a stamp catalog to more carefully identify and value them.
Realistically, an unused copy is barely worth 4 cents. A used copy is worth virtually nothing.