Years ago I used a price book. Now I mostly keep prices in my head.
If I’m planning to buy something out of the ordinary, I check the price and jot it down in the Notes app on my phone. Then I look for sales or check another store. For example I’m now interested in some different spices. I have Publix prices of several brands on my phone and will check today at Aldi to see if they are available and if so compare the prices.