I would say its just based on the value that you feel is conceived.
As far as $79 a month, that's not really anything too high in fact its probably mid range in my experience. I think it depends on competition and how many Dojo's/Dojang's/Kwoons are in the near vicinity.
There are quite a few Schools in this area that are charging $100 plus a month.
But I would prefer more of a Lai Si policy, as opposed to tuition costs. But we have to realize that regardless of the Teacher's best intentions or not if they have a professional Martial Arts School than it is a business, and has various expenses incurred.
So to make a long story short, I would say is money the only factor involved?
In other words do you feel you would gain something from the training, as opposed to going down the road for $50 a month. Or maybe the $50 a month has more knowledge or is a better Instructor, or etc...
So I would say if its worth it, than yea I would pay it but if not then keep shopping.