Billion Prices Project

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.

No data seems to be available though some pretty graphs.

Data may be coming from http://www.pricestats.com/ (a closed, paid-for source of retail data) as BPP state on home page:

If you are looking for more high-frequency inflation data across countries and sectors, please contact PriceStats, the company that collects the online data we use in our research initiatives and experimental indexes.