That would be Scott number US 1898A. It can be purchased for 20 cents mint and 15 cents in used condition.
The US has issued many dozens of red 3 cent stamps. It will take a bit of work to identify which stamp you are referring to. I would recommend spending some time looking at a US Postage Stamp Catalog to identify the specific stamp. The bonus is that most catalogs will give you an idea of value.
Red cross
2012
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.
Scott #702. Fairly common this 1931 stamp has the minimum value, meaning it is priced based on the cost of cataloging and stocking the item. You can purchase these new or used for 20 cents.
30 cents
The value of one Anna red stamp is 20 cents. It is much higher on Ebay.
The US has issued dozens of George Washington stamps, many with a value of 2 cents. You will have to completely identify the stamp to find a value. A catalog, available in most libraries can help you determine the value. Chances are a dealer won't purchase a single stamp unless it is worth more than a dollar or two.
This is part of the Washington bicentennial issue of 1932. A dealer would charge 10 to 25 cents for it , mint or used.
George Washington and Benjamin Franklin were the first two individuals. Washington was honored as the first President. Franklin was honored for being the first Postmaster of the United States.
The value of a one penny red stamp is an estimated $1.50 or even less depending on the condition. They can be purchased on eBay.
1,000,000$