I've been reluctant to post on this topic for a while because the participation is admirable.
But the thing is prices are
subjective to the consumer not
imputed by the retailer and producer. So at all those stages it's dependent on the opinion of dozens of people not mentioning taxes, regulations that differ from state to state.
That's the whole premise of inflation your money becomes worth less because it is seen as there being more off.
Now with regards to your experiment. Your item pool is too big if inflation is what you are after not other market fluxuations. I would recomend removing any subsidized commodities as that it's self causes inflation but won't be reflected in the price.
These would be: Beef, Cereals (corn, wheat, etc), Sugar.
Toilet paper & potatoes are US produced and stable staples. Peanut butter is stable but imported.
Also with regards to price sourcing you would need a wider selection of several different stores and take the average of those as your price. (removing the SALE issue).
Now getting the kind of results you want from this is going to take a lot of time. but what you will be able to see (and which would be entirely fascinating) is: "Temporal Monetary Disequilibrium"
Say Special-K lives next to the head Boeing manufacturing plant & office (a massive recipient of your freshly printed dollars) His staples would inflate faster then J'mac's who lives far away from that new money, and the people around him have not had that "wow there's a lot more money around" moment.
Picture the US as a big pond and you are throwing pebbles in it, the ripples are the prices adjusting to you adding more to the mix.
