It will vary depending on the country and year. Some are more sought after than others. Some were produced in large quantities and so have limited value beyond the face value. You will have to consult a stamp catalog to see if what you have as value.
You can find books on Historic stamps of America 1978 Postal commemorative society on en.allexperts.com/q/Stamps-Philately-1610/2009/2/books-stamps-great-grandfather.htm
You can find 1978 Commemorative stamps of America on about.usps.com/who-we-are/postal-history/stamps-postcards.htm
The ones purchased from the US Postal Service include the stamps.
Commemorative stamps are typically not sold in stamp machines, as these machines usually dispense only definitive stamps, which are intended for regular postal use. Commemorative stamps are often released in limited editions and are usually available at post offices or through specialized retailers. However, some postal services may occasionally offer commemorative stamps in limited quantities at specific machines during special events.
Medallion stamps are typically issued by governmental or postal authorities as a means of validating postage or as a form of collectible item. In the United States, for example, the United States Postal Service (USPS) is responsible for issuing official postage stamps. Additionally, some specific commemorative or special edition medallion stamps may be released by local or regional postal services.
This company produces a variety of products. Their first-day covers are real enough. I think they make gold or gold-plated replicas of certain stamps, which of course, are not real postage stamps. They offer some stamp and coin combinations that contain real US stamps and coins. I think they all sell at a discount of the secondary market.
The cost of postal stamps are $0.28
In the U.S. Postal Stamps are 42 cents each
It may be purchased online from StampsForSale which has many commemorative stamps. You may also shop at RoyalMail which has a variety of gifts and stamps.
Stamps typically come in various quantities, including individual stamps, booklets containing multiple stamps, and sheets that may feature several stamps arranged in a grid. Additionally, some postal services offer rolls of stamps for high-volume users, which can contain dozens or even hundreds of stamps. Collectors may also find stamps sold in specific quantities for special issues or commemorative releases.
H. D. S. Haverbeck has written: 'The commemorative stamps of the British Commonwealth' -- subject- s -: Commemorative postage stamps
Its a post office, so anything postal from stamps to envelopes.