The Billion Prices Project is an academic initiative that collects prices from hundreds of online retailers around the world on a daily basis to conduct economic research. We currently monitor daily price fluctuations of ~5 million items sold by ~300 online retailers in more than 70 countries. This webpage showcases examples of average inflation indexes that we created to illustrate the type of statistical work that can be done with this type of data. Our team is currently working on developing econometric models that leverage the data to forecast future trends and conduct economic research. http://bpp.mit.edu/
I went to the website...they say they get the information from 53 different retailers but dont say which ones. Judging by the low rate of inflation they have for the USA, I'm guess at least 10 of those retailers are electronics retailers where prices always drop over time. The site doesnt list what retailers only saying its a "broad" range. Until they explain what retailers they have, I wouldnt trust any information on that site.