Margins vary from tea to tea and are generally slim. There are some teas that I expect to lose money on and others that have slim margins. I'm assuming that marketing the service as less than a dollar a day will go a long way in giving the "affordable" signal.
Since all tea is shipped on the same day and bought in bulk, I'll have to rely on volume to make it a profitable business.
With respect to the amount of tea, I, as a tea drinker, drink multiple cups of tea per day. I figured one cup per day for subscribers would be the ideal way to go.