I have been attending Tibetan Buddhist meditation and teachings at a monastery for several months and am enrolling in a foundation class next month. They suggested a voluntary offering to the teacher for this class, however I want to make sure I offer something appropriate. I'm also not sure if it's a "one time" thing or if something every class is suitable. I searched the web as well as the forum for this information and couldn't find anything regarding this question.
Money is the standard offering and has been since at least the time of Lord Atisha.
However, actually using the teacher's teachings and doing what they say to do is the supreme offering.
"Neu-sur-ba said: You must see any affliction as an enemy and attack it as soon as it arises in your mind. Otherwise, if you acquiesce when it first appears, and then nurture it with improper thoughts, you will have no way to defeat it, and it will conquer you in the end.”
-Lam Rim Chen Mo eng v01 pg. 348 tib pg. 275