Hmm, maybe I am simplifying this but can't you do:
Fraction that convert to paying * How much they per on average per month * Average months before cancellation * Some sort of Discounting for value of future money (unless you plan to increase price) = value per member
For avg months before cancellation count all those that are yet to cancel as 2x there lifetime (seems reasonable). Would give you a fairly reasonable guess. Then you just have to make sure that the value of a paid member is the same.
Comments
Hmm, maybe I am simplifying this but can't you do:
Fraction that convert to paying * How much they per on average per month * Average months before cancellation * Some sort of Discounting for value of future money (unless you plan to increase price) = value per member
For avg months before cancellation count all those that are yet to cancel as 2x there lifetime (seems reasonable). Would give you a fairly reasonable guess. Then you just have to make sure that the value of a paid member is the same.
discounting: http://en.wikipedia.org/wiki/Discount