Creating an iPhone and Blackberry application

I would like to create an application for the iPhone and Blackberry that would allow users to see the cheapest gas in the local area. I would like to focus primarily on Canada, and Europe if possible. The app should list where the cheapest gas is within a certain. The user will enter the range (so let's say 100 kilometres), and the application will then show the results, from cheapest to most expensive, and the distance required to get to said location and what city/town it is in. The iPhone also has a GPS, so the application should hopefully be capable of integrating with the GPS to give specific directions once a gas destination has been chosen by the user.