I saw 15 basic models selling for €100 under msrp during black friday on one retailer in Finland.

well iphone 15 is already cheaper than 14 was at launch so.

September 2024 when the iphone 16 is launched.

iPhones are so mature by now, I do not expect huge inovations - so you can use them basically until software updates stop. So every year you do not buy now, reduces the useful lifespan that you can get out of it - not sure that the price reductions, which will come until iPhone 16 comes out, compensate for the reduced useful lifetime.