nostr:npub194h76frd3mdsp67fn85kdemcn8m0ur5e6qcflnwwap9q25gwj96qdj4ewx AFAIK Supermarket chains (& some other big chains) have had differential pricing by store (probably store segment in practice) for at least 30 years (learnt hard way, Boots, Bootle).

Presumably website prices (excluding Nectar/Clubcard/...) are universal & change over time is what is most interesting. Could do a lot with a sequence of online shopping bills and/or scanned bills. Use #OpenFoodFacts to assist product matching (although IRI had a team of ~16 ftes doing this in the '90s).