I am working with hard drives. For simplicity, let's say all drives have the same capacity, 1TB and all cost $100.
They typically last about 4 years, when they need to be replaced. They drop in price about 50% over that period of time. They cost 100 dollars for the first for years, $50 for the next 4 years, etc.
What's the usual way of estimating the cost of something like this?