Of course this whole conversation is relative to location and supply and demand. In our area $20.00. is the norm. The chain studio that we go to offers either $25.00 a group lesson or a group pass for $100.00 for the month and you can go to as many as you want... Usually with 2 classes offered a night if you plan it right it could be economical.
Being a married couple we do not do group classes because for a single class it would cost us $50.00 while for just a small amount more we can do a a priviate lesson. Again, in our area a priviate usually runs around $80.00.