Costs of creating an iPhone application?

[Will]

Hi I'm at University I am currently doing an Enterprise & Entrepreneurship project. We have to come up with an idea to present to a group of people. Its similar to Dragons Den. The idea our group have come up with is an iPhone (or any phone app) that allows the user to pay for petrol at a station without having to que up inside and pay there. It allows the user to swiftly pay for petrol and move on and makes the whole process of being at a petrol station easier. The way the app works is that it is similar to pay and go pumps you get. You set up an account with the petrol stations (we are using shell) and you can prepay for petrol. You tell the app how much you need or budget. Then you pay and are given a receipt code that when you reach the pump, there is a computer screen that we have to install that you enter your receipt code and then it gives you the amount of petrol you have paid for. You then fill up your car and drive on. Simple? My role in the group is finance and I have to find out costs of bringing this all together so that when we pitch our idea, we know how much money we need to borrow off them to get the idea off the ground and into the app store and onto peoples iPhone. I know I will need to pay for an iPhone developer and to put it into the app store and also to add the access point at petrol stations but I don't really know how to find this information. I have looked on google but haven't really found anything. Can anyone on here please help?