Some products' prices stay the same. Others change every month, some every week, and some products can see price changes on a daily basis.
The price for this printer changes drastically multiple times a week. In mid September the price saw a 148% increase, and then over the course of the next month gradual decreases to an all time low that was just 60% of its price.
But it's not just printers. These cables jumped up 163% of their price overnight and then dropped to 61% of that just a few days later.
Some products have prices that only fluctuate +/- 2% of their average price. But the only way to tell is by viewing their price history. That's why it's important to check the price history of a product before you buy. You may be getting a great deal, or you may be paying more today than you would have paid yesterday.