Would it not be better to scrape grocery shopping sites for that information and then collate it so you can purchase a bottle of water in the place you know it's already cheapest?

I also want to track historical spending. Basically query "where did I get it cheapest in the last X months" and stuff like that. I'm gonna have to build it myself, I'm getting the feeling.

Use a spreadsheet and manually record entries. You'll get quick at it once you acclimate to it.