It is good idea to invest in crypto currency but you should know your limits, if you are lucky you will make money.
RULE OF THUMB - "Always invest amount of money that you can afford to lose".
You can't predict future so try to avoid speculations that you will invest 300$ every month to become a millionaire some day, ultimately, you will end up thriving to become a millionaire without knowing whether you will ever become one or not. It is better enjoy your present i.e. earn your daily bread and some beer :) and enjoy with your loved ones.
You can even become millionaire with 12$ if your destined to, read https://www.cnbc.com/2017/06/20/bitcoin-millionaire-erik-finman-says-going-to-college-isnt-worth-it.html
RE: What percentage should you invest in each cryptocurrency to become a millionaire? A guaranteed winning strategy (updated 8/19/2017)