You will need to consult the catalogs and do some research. There are lots of stamps issued and they vary in value from almost nothing to some nice values.
Most libraries will have a copy of Scott's Postage Stamp Catalog of the World. First of all, you have to identify the specific stamp or card. That in itself can be a daunting task, but most of the catalogs are well illustrated with lots of information. Once you know what item you have, the catalog will provide a set of prices that can be used to estimate value.
The cost of postal stamps are $0.28
How much is postage stamps in 2012
The cost for postage in 2005 was 37 cents.
The prices of stamps changes quite consistently over the past few years. In order to stay updated, I would visit the USPS website to see current prices for postage stamps.
42
they cost $0.49
18.5
500 first class stamps would cost: Well it depends where you get them from!!! :)
What is the current cost of a stamp on a first class letter under an ounce mailed in the US? <><><> 44 cents
37 cents
$8.80
$44.oo for 100 stamps at $.44 each