[shawnreilly]

You need to determine the cost per User. Different Users might represent different Usage Patterns, so I'd be looking for averages. If the Product is already in production and you have an existing user-base, this is how I'd do it; Correlate your user-base statistics (number of Users) in relation to your hosting costs at different milestones and/or points in time. This metric will give you some insight into how much it costs per User at different stages of growth. This could include the growth of the user-base as well as the growth of your Product (in terms of features and/or infrastructure changes). You would want to identify any trends and/or variations with the resulting averages over time. This will give you some data to work with in terms of making projections.