Why Does Cost of Living Change?

Just trying to find an answer to this question, why was the cost of living much cheaper in the 60’s compared to now and what caused the price increase?

For instance, my grandad said when he first cam here to Detroit from the south, he only paid $40/month for his apartment, this was the late 1950’s. But now it would be hard to find a decent apartment for $400/month. Four hundred a month might’ve bought you a palace back then.

What made the same things people had then much cheaper than the same things people have now?