Work out the cost per cup of loose leaf or bagged tea.
Tea is costed by yield, and yield depends entirely on the dose. The convention is 2 to 3 g per 200-250 ml cup, so a 125 g pack gives around fifty cups at 2.5 g — meaning even a six-dollar loose-leaf tea lands near thirteen cents a cup. That is why comparing tea by pack price is meaningless: a dearer pack with a lighter recommended dose can be cheaper per cup than a bargain one. Bagged tea removes the choice, since a standard bag holds about 2 g fixed, which is also why loose leaf tends to work out cheaper for anyone who brews strong. Good leaf will also take a second infusion, roughly halving the cost per cup again.
Tea cost by yield
Cups per pack = pack grams / grams per cup; cost per cup = pack price / cups per pack; yearly = cost per cup x cups per day x 365
Usually per cup, because a bag is fixed at around 2 g of lower-grade dust and fannings while you control the loose dose. The saving is modest in absolute terms — pennies a cup — so quality is the better reason to switch.
Close to half, if the leaf supports it. Most quality green and oolong teas give two or three good infusions; black tea and anything bagged rarely give a worthwhile second.
It is real but small — under a cent per cup if you boil only what you need. If you routinely fill the kettle for one mug, the energy can rival the cost of the tea itself.