have you searched the certification options here? There is one online barre certification https://www.ideafit.com/events/organization/bar-fitness/online-ballet-bar…. By their description, it is the only online certification but nowhere near the price tag you are looking for.
Please consider looking at non online options. I think one gets a lot from working with an actual teacher… getting feedback, and getting that kinesthetic piece. Are you near Boston? There are so many good programs available in the area, you might find something that works.
For me the question is always what is the BEST training that is in a range I can afford. I once chose something because it was convenient and online and was so disappointed as it was badly done and carried no weight in the industry.