Like everything on the internet, prices at Amazon vary by the moment. They have a very complex algorithm based on your web browser history, what you have looked at, what you have bought in the past, what you bought from other vendors, and what people with a history/profile similar to yours have bought.
The longer you let it track you the more reliable it becomes at predicting you.
Years ago when I first used Amazon, I bought a large set of vise grip pliers, to hold things when welding, and some supplies for the plasma cutter, and little wire feed welder. Every time I logged in to my account, I got a bunch of recommendations for locking pliers, and welding supplies. Which of course I didn’t need, because I had already bought them. As I have continued to buy things from them their recommendations have gotten better.