You never know when it's going to change. I am always getting notices atop my shopping basket (where I keep 100 items, watching for when someone's going to have a used copy cheap) that say, "Since your last visit, the price on 098769765 has increased (or 'decreased') from $0987 to $0912."
They are obviously always weighing what they can afford to sell for -- according to ?wholesale price? - ?amazons-current-cash-flow? ...
But I've never got caught in middle of price changing like you seem to have.