Excel 2007 : How to create 'start and date' input?

I am creating a spreadsheet for car hiring company. I want to create a start and finish date in which the user can specify which date they want to hire the car and when they want to finish hiring. Also, I want it to calculate the total cost and if it is possible to link to the multipliers. I have attached a spreadsheet for you to look at. Could you please give me or point out instructions please? Alternative ideas are welcome.