Does anyone know where i can get a gentex shg, preferably under 100 bucks

I want to add a gentex shg to my collection because they are discontinued, if i cant get one i will have to wait for my school to replace their system so i can get a shg they have.
Gentex shgs are my favorite alarms, and i want to get one for christmas this year of if its cheap enough get it in a few weeks