What is the value of a Confederate 5 dollar bill?

Assuming it's genuine, depending on the year, design, and condition its value could range from about $4.50 to $1800.00

However the vast majority of "Confederate" bills found today are actually replicas sold in souvenir shops or included in memento sets. Those made within the last 35 years or so are required by law to have a Word such as COPY, FACSIMILE, or REPLICA printed on them but that's usually absent on older ones.

Most replicas were never intended as counterfeits but a lot have ended up on the market because they are often very difficult to tell apart from the genuine item. Many of the copies are printed on artificially aged paper using photo-lithographs of genuine bills. One check is to look closely at the signatures - the ink is flat and on the surface of a replica, while it is a slightly different color and more deeply impressed on a genuine note.

The Related Link has a list of serial and plate numbers found on the more common copies; you can compare those to the numbers on your bill. If they don't match you should seek out a dealer or appraiser who specializes in Confederate currency and have the bill examined in person