Too late. A promotion just ended July 15th that allowed subscription customers to migrate certain products for free. I believe AutoCAD Mechanical could have been migrated to Autodesk Design Suite Standard, Autodesk Building Design Suite Standard, or Autodesk Infrastructure Design Suite Standard. These "standard" suites include base AutoCAD.
Maybe you can check with your reseller/channel partner to see if you can still get the promotion.???
Start with some of our most frequented solutions or visit the Installation and Licensing Forum to get help installing your software.