hmm I can understand your frustration. I have not checked but is mental ray included in the student version of maya? If so I have included a screen shot of where it should be. In version 2013 of maya it is on it's own section in the plugin manager.
I have included a screen shot. I am not sure about how it is on a mac though.
If you cannot find it in the plugin manager go to the maya 2013 folder and see if there is a mental ray sub folder to see of it was part of the installer for the student version. Not sure what else I can offer. Best of luck though.
"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675