The MCM registration site is now open, and for the first public rotation the price is 50% off..

http://www.microsoft.com/learning/mcp/master/register/default.mspx 

Here are the prereqs for the Active Directory MCM:

Also you must have at least the following:

You must have the following exams below completed in order to qualify for the Microsoft Certified Master: Windows Server 2008: Directory.

Pricing structure

Nonrefundable program application fee: US$125
Program fee: US$18,500
Non-lab exam retakes: US$250
Lab exam retakes: US$1,500

Note The program fee includes the price of first attempts at passing all required tests, including the final lab exam.

Participants who attend the first public beta rotations (training program and exams) will receive a 50 percent discount. Public betas for Microsoft Exchange Server 2007 and Microsoft SQL Server 2008 are scheduled for October 2008. The Windows Server 2008 Active Directory public beta is scheduled for November 2008.

Good luck, hope to see you in November...

-Chris