Around $50 a month for my portion of the family plan I'm connected to. I am not the primary line, however, so my line was only $10 to add.
$10 line fee with an undisclosed amount of minutes(insignificant since one: I don't rightly remember how many we have and two: we have a ridiculous amount of rollover minutes)
$30 Unlimited Data plan(Yes, Grandfathered. 🙂)
$5 Unlimited Messaging plan with free Mobile to any Mobile calling ($20 for the whole family plan, divided by five since I only pay for my portion)
+whatever taxes they collect for the bill divided by five. I just told my primary that I'll shoot them $50 to cover my portion and they agreed.
EDIT: One more interesting thing about the contract we have set up, although I know a few more people here might have the same thing:
My line is only $10 while my primary's is almost $30, but instead of have an 18month hardware upgrade cycle like me, theirs is every 12 months.