Be careful about resorting to a co-author. You can easily find someone who is a fast writer and good with grammar but also consider writing style. Everyone writes a bit differently and has a unique voice, and sometimes it's hard to collaborate so that someone's writing style matches with yours. The only co-author written works I did were roleplays and even then you could sense that there were two different authors for it.
Be careful about resorting to a co-author. You can easily find someone who is a fast writer and good with grammar but also consider writing style. Everyone writes a bit differently and has a unique voice, and sometimes it's hard to collaborate so that someone's writing style matches with yours. The only co-author written works I did were roleplays and even then you could sense that there were two different authors for it.