Story points are the currency of Agile and they are used for estimating User Stories. These estimates give you an idea of the relative size of different User Stories. You can use this information when making decisions about prioritization.
In the initial proposal we sent you, we gave an estimate of the effort required on our part to complete a Story Point's worth of features (based on comparable prior projects). This number is an estimate, as every project is a little different. A Story Point is typically 1-2 hours of work. As your project progresses, we'll have actual metrics showing how much effort is required to deliver a Story Point's worth of features on your project. We'll use that information to project the remaining cost of your project and we'll share that information with you in your project status report every week.
If you want to think in terms of dollar amounts, you can always ask your project manager what the current cost per point is on your project.