@2d6fed24 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). 

 @8498c3c0 the code from that thread was open, so could  reuse that to scrape website data. But agree with you that there's interesting additional observations to come from local data.