Depends where in Cincinnati you need to go. Dayton is about an hour to an hour and a half north of Cincinnati, and even farther from CVG, because as we all know, CVG is actually in Kentucky.

Don't know anything about shuttle buses, but you can probably rent a car and not have too hard a time finding Cincy from the Dayton airport. If that's not an option, I'd do a search for the DAY website, and check the ground transportation options. Or just have someone pick you up at DAY. Good luck.