It is really upto you on how mucb money are you going to take a risk.
How much money are you ready to loss? because in trading you don't know what will happen, you will either lose or gain profits.
As for me I started with $30 dollars just to try it out and make some experiments to know what mistakes I could possibly make So thay I can plan my strategy really well.

Now, I invested $250 dollars, so that I won't miss greater profits. as you may know the larger you invested the higher the risks with a higher profits.