Best I can do is wish you luck on this one. It is unfortunate that many powers-that-be are requesting such estimates on what is essentially a level-of-effort job. What they don't understand is that, much like the job of PM, it requires your constant vigilance for immediate action.
Reminds me of a time when the Program Management Office wanted me to provide them with a six-month CM schedule. I tried to explain to them the uncertainties of CM activities. With their "we-ain't-giving-an-inch" attitude, they simply didn't hear the parts about "it depends on the source of activity, ECP, TPR, etc., the nature of the proposal/request, the complexity of analysis required, etc."
What finally got their attention was: "You give me your schedule for your next accident, what it will be and the damages to be incurred; and I will give you a schedule for CM activities."
Now, if you're talking about setting up a CM program, that can be broken down into such tasks as "how long to write/develop the CM policy, the CM plan, CCB charter, Issue reporting template, individual procedures documents, etc.
