There is - or used to be - a site which showed previous prices, so you could look at the price of e.g. Twinings Lemon and Ginger Tea $7, and see when it had last been as low as this.
I've been racking my brains to think what it's called. Any help, please?
https://pricehipster.com/?q=Twinings%20Lemon%20and%20Ginger%…
Price Hipster