How much does platinum need to be discounted in order for you to buy it?

For me, I buy every time it's 75% off. They haven't seemed to catch on that I've done this literally every time for the past decade given I've only been offered it less than 10 times. The base plat prices are highway robbery and I would never buy at that level. Anyway, what discount do you wait for in order to buy? How often do you get discounts?