You can even trade with $10 if you time the market right. In a bull market such as the second half of 2017, $10 on almost any small cap used to unfailingly yield 10x profit. If you're leaning towards safe trading on established assets, I'd recommend a minimum of $100 to start with.
Do not put in what you cannot afford to lose and carry out due research before taking a position on obscure coins.
Starting trading with a small amount for me is not challengeable, you could not earn with that certain amount you must have a big capital for better profit you have. 100$ for me is not enough for trading you should have a big capital because there is covering the fees when you doing to trade. More coins you trade the more profit you have so much better bigger amount of the great start in trading.
If you are in trading give your best in doing analysis and deep research in every coin you purchase making an error is made a mistake an lost.