Price Comparison Site

I wish to monitor the prices of items in my local supermarkets and stores so require an app that will scrape data such as store category, the product details such as brand, name, weight/quantity etc. and prices from their online stores. I want the app to check prices once a day and keep a history of price changes and their dates. The same products will regularly exist across different sites so they need to be linked. The item names should be searchable and displayed in an easy way to compare current prices and see historical data with an accompanying graph to show trends. User Story: I am in a shop and see a product I would like to buy. I want to to know if the price it is being sold at is good - i.e. is it higher than average, a great deal or being sold at the average price? I want to be able to search on the app to see what the current prices are for the product across other stores and see what the historical prices have been. I want to be able to scrape this data from multiple difference online stores however the MVP only needs to query data from one store. I expect there to be a requirement for approx. 20 different sites so within your bid comments I would like to know how much you would charge for adding additional sites and also making updates to existing sites should changes be made that break the scrape. Some examples of existing sites that this app should be comparable to are: [login to view URL] [login to view URL] This should be a web app however after the MVP has been created the second phase (and separate project) will be to add new sites and then create a mobile app.