It's always hard to decide what to charge for knitting, especially when it is your friends who are the clients. The old rule used to be double the price of the yarn, but some charge 3 times the yarn now. Or whatever you can get. :-)
For lessons I don't know. I know some folks pay a lot for lessons, especially from popular teachers, but I have never charged anything. It is safe to say you aren't going to get rich this way but you could make a little spending money. Private lessons ought to be worth a little more but if you try it as a group, if they each gave you five dollars, you'd come out pretty good. I think it depends a bit on the economic status of your customers. As long as every body is happy, it works.