I hope you enjoy the class. If it's an introductory class I'm betting most of your class work will be learning to make rolls. There are 3 basic knives for most Japanese sushi cooks. Debas, Usubas and Yanagibas.
The key knife is the yanagi. It's used for thin slicing fish and could be used to process fish too in a pinch (this is a deba's main task but I doubt you would be doing much of this).
The Usuba is usually used for vegetable prep but again you could get away with using your yanagi for this if you want just 1 knife.
So here are a couple yanagis in that price range I really like.
Kaneshige 240mm Yanagi is made with carbon white #3 steel and is really nice. One of the best values considering it's hand made in Sakai and much better than some of the cheaper yanagis that are about the same price range or less.
Kaneshige 240 yanagi: http://www.chefknivestogo.com/kawh3ya24.html
If you want a good stainless steel yanagi I recommend the Saji. http://www.chefknivestogo.com/tasa24yaho.html