I'm undecided about getting into the collecting of encased stamps, aka encapsulated stamps, or stamp currency. There was this one-year Civil War period in US history when stamps were used as coins. Does anyone collect or know about these? I'm not a Civil War buff, but I am a collector of both stamps and coins, and I seem to remember from long ago that these things were worth collecting, but perhaps only for historical reasons. The one is question is an Ayers Pills coined stamp.. What is their value? Are they rare? Are there fakes?
You should find a copy of Scott's US Specialized catalog and read the section on encased postage stamps. Condition is very important for the prices listed in the catalog.
Other countries have also used encased postage stamps as coins but off the top of my head I can't think of a worldwide catalog for them.