There are all kinds of kits available to the beginner. I also run a mirror making class in the San Diego area and I usually have the guy bring in just a single piece of glass for the project. I supply all of the grits as part of the class supplies.
You should probably talk to the class supervisor as to what you need as in my class, you keep all of your grits, etc. at home as they aren't needed.
Grits, when bought in large quantities are so cheap that you will probably not even use up $2 worth of grit on a 8" mirror.
In addition, you might want to talk to the supervisor as to what size he will prefer you to make in the class. For a beginner doing the whole thing by himself, a smaller mirror (6" or 8") is a good choice but if you have the necessary assistance and are willing, a much larger mirror can be done without problems if the supervisor allows it.
Pregenerated blanks make the sweating part of the initial grinding easy as you don't have to hog a hole into the glass by some means although for an 8" mirror this is usually done in 2-3 hours of work with a ring tool. After that comes the casting of a tile tool followed by the grinding down through the various grits and finally polishing and figuring the mirror. That initial work is your choice like everything else.