You have had a reply to the same posting here
The other (short) answer is it depends since your costings will depend on the issues that Don indicated. Since the decision has been made to go with Moodle, the remaining questions are how to implement it (hosting, training, etc.) If you have the time to do a pilot, you could learn a lot with a pilot implementation with evaluation. Some Moodle Partners have different levels of hosting where you could grow into the implementation over time.