It’s the exact same seat on the exact same flight. The price you see isn’t really about the seat — it’s about you. Flip the signals a website can guess about you and watch it move. (Illustrative figures; the real formulas are hidden — that’s the whole problem.)
You changed nothing about the product — only what the seller could infer about you — and the price swung by well over a hundred dollars. That’s surveillance pricing (also called personalized or dynamic pricing): the figure on the screen is shaped by your device, your location, your history, your urgency, and how committed you look. Some of these are documented (a major travel site once steered Mac users to pricier hotels); others are illustrative. The constant is that you can’t see the formula — so you can’t tell a fair price from a profiled one.
A teaching model — figures are illustrative, not a specific company’s. No accounts, no tracking, nothing leaves your device. Free to copy and reuse (CC0).