If you have $100 right now than just invest that in some promising ICO which is currently open for investment. You might get more than 10x return within a year if that project got successful. Look at Monaco for example, price has skyrocketed after few months of their launch.
Totally agree. I also think that you should only invest in projects in which you really believe. Otherwise, you will be panicking every time the price drops. If you believe in a project, you will HODL no matter what, and guess what - this is often the best decision. With 100$, probably the best option is a promising ICO or a coin that has just been released on the market.