Millions of dollars. It would be a One-of-a-kind, but it would have had to gone to the Moon and back. Therefore it would have to be certified and authenticated.
The coin has been altered and has no collectible value. This is not an Mint error.
This would depend on what year it was issued and the condition of the stamp. For example a used stamp in average condition from 1998 is worth between 6 and 19 cents to a collector but could not be used for postage. An unused stamp in average condition from 1998 would be worth face value; in the case of a forever stamp (without a face value printed), it would be worth whatever the current postage rate has been raised too (as of January 2013, it would be worth 46 cents) and could be used for postage at that value.
Face value if it hasn't been used.
A variety of stamps have been issued during the reign of Queen Elizabeth II. The 4D Queen Elizabeth stamp is worth between .75 and 1.50 pounds.
A real triumpth in stamp history and should be worth at minimum £80
The value of these stamps is usually $6.00 per stamp. Scott specialized catalogue I have a complete booklet of stamps, 50, mounted as purchased in 1943, with my signature and other descriptions and details on the covers. Does this make the booklet and stamps more valuable? What would be the best way to sell it, if I choose to, by auction or which method?
If the stamp has been used, the post office will tell you it is worthless. If a stamp has not been used, they will tell you it is worth whatever is on its face value. The post office will not appraise a stamp for its collectable value.
That will depend on the specific stamp. Consult a postage stamp catalog to identify and value the one you have.
Everyone hopes to come across the "Old Stamp Collection" that had been sitting in the closet for years. Bring the collection to a local dealer for evaluation. It will be a modest fee but it could be worth the charge.
In 1990 a first class stamp was 33 cents. A post card would have been 20 cents.
That will depend a great deal on which 15 cent stamp it is. There have been stamps issued for many decades with that value. Consult a catalog and identify the specific stamp. It will also help you find the value.
Martha Washington has only been pictured on four cent or eight cent stamps. They would be Scott numbers 636, 556 and 306. Consult a postage stamp catalog, they all have some nice value in mint condition.