$50 is a very low money to start in investing. I prefer to you to join in some signature campaign and you can earn a small amount of bitcoin or just go in the trading but in trading there is a high risk.
And most of the time you won't even get he minimum required amount for trading with 50$. Might as well play dice with it and hope to double that before thinking of trading. Or as you've said, keep that amount still and earn btcs to add to that.