What a supermarket bag actually is
Usually CTC black tea — leaf cut into granules that extract fast and give strong colour through milk — blended for consistency and sold without an origin. Judged as a delivery format it does its job well, and dismissing it is a mistake. What it cannot do is be re-infused, vary interestingly, or taste of a particular place, because none of those were what it was built for.
What you get for the extra money
Three things, in descending order of reliability. Provenance you can check: origin, harvest year, cultivar, processing. Multiple infusions from the same leaf, which changes the cost per cup considerably. And variation between harvests, which is either the appeal or the annoyance depending on temperament. What you do not reliably get is more caffeine, better health outcomes, or any certainty that you will prefer it.
Where the money stops buying much
Price rises steeply at the top of the market for claims a buyer cannot verify — old-tree material, plot numbers, competition grades, pre-Qingming picking, ages on pu-erh wrappers. Some of these are real and none is checkable from outside. A well-described tea in the middle of a merchant’s range is almost always a better purchase than the top of it, particularly early on.
How to buy without being sold to
Look for specificity over adjectives, and for sellers who describe rather than promise. Small quantities from several vendors beats a large order from one. Samples exist and are the cheapest education available. If a description leans on rarity, ceremony or wellness rather than on what the tea is and where it came from, that is a signal about the seller rather than the leaf.