Today I found an interesting article on how much will your SOA cost from David S. Linthicum. His method is a good indication for the total cost. During the realization phase I will use scrum to determine the productivity of the team and to manage the expectations of the client.
One off the elements in SOA projects is estimating the cost. In classical Designer/ Developer projects we use function points to estimate cost (#function points * hours per point). In our current SOA projects we are using our experience from earlier SOA projects and we are using Scrum. The interesting point off Scrum is that the team makes a relative estimation off storypoints, use cases or requirements. After this relative estimation the storypoint, use case or requirement that is most clear is estimated into hours based on past experience. The rest is than calculed from that reference point. This method is good emperical approach and is fun because we are using planning poker.