From my opinion with $100 u couldn't invest in anything because the rate of exchange is too high now maybe you could buy some eth but the invest that you put there not optimal. If i were you i will invest on the new ico, most of ico sale their first token with some bonus and the token price some of them under $1. But you should analysis the ico first, will the ico have an opportunity to success or not because if not you will throw away your money without gain anything.