Think pads get ordered by companies in bulk. After a few years, they get swapped out for a newer model. The old ones often get resold to a refurbishing company, and they test them and sell them refurbished for way less money. This happens a lot, so because they are refurbished and there's so many of them, prices are extremely low. I got like 6 of them for 200€ each. It's insane. So that explains the extremely cheap ones.
I could hypothesize that the price jump is because there's a gap between new and refurbished models, but tbh I don't really know and I also don't see that much of a jump. But that's kind of my theory. Hope that helps.