The US Bureau of Labor Statistics actually employees quite a few people to call stores across the country and get prices. Planet money interviewed one such person not long ago. https://www.npr.org/2021/07/13/1015804773/how-do-you-measure...
If someone actually finished working on an inflation database website I would love to enter data for them. I'm seeing spikes across everything I buy in the last 2 months. I feel like the true inflation for food itself is at least 33% in the last 5 months.