That's supply and demand I suppose. As demand for lightning dwindles due to a decreasing number of people actively using devices with lightning ports, the price will tend to drop. That's not an invalid reason to prefer lightning over USB-C, but it's not sustainable. Production of lightning accessories is probably at or near 0 at this point so the oversupply will not last forever. Enjoy the deals while you can!
The cables tend to cost the same, way more than the cost of manufacture.
If you're buying them in bulk on amazon, usb-c is still more expensive than lightning, but the vast majority of people tend to buy cables when they have either lost, forgotten, or broken their existing cables. Go to a shop at an airport or train station and they'll charge you £20 for a cable, and people but them.
The "apple tax" is irrelevant to the actual amount paid.
