This article is from the Paper Money Collecting FAQ, by Bruce Giese email@example.com with numerous contributions by others.
Yes, this is a major area for collectors and many people
focus on CSA notes. Lots of them are very affordable.
BEWARE, however. There are numerous copies of the Confederate
notes, including packets of copies sold at popular National Park
battlefields. Many can be identified by the serial numbers alone.
[Note that CSA notes are contained within the World paper
money section and not the USA paper money section.]