February 1926 is when the 10¢ airmail stamp was released. The olive brown 15¢ one was released September 1926 and a yellow green one for 20¢ was released January 1927. This stamp was designed by C.A. Huston with a map of North America with a De Havilland DH4 on each side.
All 3 stamps were issued to meet the new Airmail rates. The 10¢ stamp covered one zone, about 1,000 miles for a 1 ounce letter.
You can research stamp prices but they do tend to change.
As of 9/2013 There were no successfully completed Ebay auctions for this item to give a range. As common as it is I've found only a few for sale and always in a set. With over 42 million having been made I don't expect this stamp to have much value despite it's condition or being a (FDC) First day cover or not.
184⁄100 x 75⁄100 inch
|Designer||C. A. Huston|
|Stamp Number (Scott)||US C7|
|Michel Number||US 300|
|Issue Date||February 13, 1926|
|Stamp Number (Scott)||US C8|
|Michel Number||US 301|
|Plate number||18746 L|
|Issue Date||September 18, 1926|
|Stamp Number (Scott)||US C9|
|Michel Number||US 302|
|Plate number||18898 R, F18892 B|
|Issue Date||January 25, 1927|