College credit doesn’t translate into publication, so if that’s the only reason you’re considering shelling out the extra cash, then you can probably find better uses for it. Publishers don’t concern themselves with how much money you’ve invested in your fiction; they’re worried about the strength and beauty of the writing, the intrigue of the story, and the depth of characterization. Whether you paid for college credit on the path to strong work—or quit your day job for a year and ate only soup in order to write, or pieced together a manuscript by writing for only an hour every morning before you left for a paying gig—won’t make a bit of difference when it comes time to accept or reject the work.
Of course, there are reasons to pay the extra money. If it affords you the opportunity to work with a writer you admire, then you might find the fee worth it. If you’re a non-fiction author and the credit helps you work toward a degree that establishes you more firmly in the field you’re writing about, it could make a difference in your credibility as an author. You might decide to put up the extra money if the course that seems the best fit for you happens to be one that is only offered with college credit.