I only send notifications to the paid version of the app. But a one time $1.99 doesn't really map to the on going costs of sending the notifications. I have con

I only send notifications to the paid version of the app. But a one time $1.99 doesn't really map to the on going costs of sending the notifications. I have considered sending notifications to the free users as well as it seams to increase use of the app which should lead to purchases/affiliate commissions. However a subscription model is probably the way to go of course.