I do not believe the markings are period or authentic. As a rule, no genuine Confederate blade has either a stamped "CS" or ""CSA" or a date. And die stamped unit identification is never on a real Confederate blade. Because of the evenness of the rust patina on the blade and markings I suspect it is artificially aged.
Here is a great resource and archive of fakes, Scrolling through it you will see many examples of unauthentic die stamped markings and artificial aging and maybe even a Bowie/short sword or 2 all similar to yours.
But $20 still ain't bad