I don't think you can make a lot of money starting with only 100$. Last year maybe but not this one. In 2018 the crypto-market has become more complicated and not that volatile. To be exact, it is volatile but only with huge dumps. The coins each month decrease their maximum price level. So, in this market, we should be now very careful. In my opinion, it is worth to start at least with 400-500$ to make a good passive income. But that is the minimum amount. I think starting with 1000$ is the best option. This way you can expect at least on 200-1000$ profit a month if you trade right.