This depends on what you compare it to. Compared it with a non-certified teacher you find through some website where any person can sign up as a teacher, and with no quality control except online reviews, then the costs are definitely higher. No professional and certified teacher would work under these conditions.
However, compared to a face to face class with a professional, certified and experienced Chinese language teacher, studying online with LTL is a lot cheaper.
This is because not only do you not have to travel to the school, but your teacher also does not. Also, instead of living in an expensive place like Shanghai or Singapore, where people go to study Mandarin, online Mandarin instructors can teach from their home towns which are usually much more affordable to live in, either permanently or for a while when they are back home.
However, at the same time the quality we offer is exactly the same as you would get a real physical LTL school. All our online teachers proved themselves first teaching at our schools for years, and all went through a rigorous interviewing, testing and application process.
Regular performance reviews, teacher trainings and incentive schemes for outstanding results happen exactly the same for online and offline teachers. In fact many LTL online teachers also still teach at an LTL school in addition to teaching online classes.