We have been buying extra strong PG Tips British tea from Amazon because we think American tea is way too weak. 3 boxes of 80 were about $40 last time I bought them a few months ago. They’re now $80. Thankfully we discovered we can get an order of 6 for $60, but we have to wait until mid-February for the to arrive. Meanwhile, a single box of the same tea, which we’ll have to get in the mean time, is $20. Yes, a single box is less than a 3-count box order, but you still save if you buy 6 boxes. How does any of that make sense?
Looking at the listing, the reason is because you’re buying from different people. The 1 pack for 20 is from Nosh London, while the 3 for 80 is from British Selections. The 3 for 40 was most likely a third seller who ran out of stock. Amazon is more a market than a store.