You are looking at a multi-faceted solution. The grocery industry is very competitive, with operating margins around 1 to 2 percent. You are going to need to learn how to tie / relate the databases together. I have a United States of AMerica based solution.
- Food products: Supermarket API will provide you with a API to identify products within a number of grocery stores, it is free for a 3-week trial
- Ingredients: Open Food Facts
- Nutritional Values: The USDA National Nutrient Database for Standard Reference provides nutritional information
- Price: The aforementioned Supermarket API will allow you access to the price, but for $1,299 per year. This is not an open data solution, but prices amongst grocers is very competitive.