How valuable is a 20 dollar confederate bill?

The note then has folds but is intact, if so you need to take it to a currency dealer. There were a lot of different $20 CSA notes, some rare some not. There are also a lot of reproductions and some were made a long time ago. If you live in a large city then you should be able to find a currency dealer. If there is a coin club in your area some of their members may also be of help. I do not have any of the guides to Confederate (CSA) currency. It is a specialized field.