It completely depends on you because how much risk you want to take. Every person will decide according to his income so even you can start with as little as 100$ but if you are looking for long term investment better invest more into crypto currency.
+1
You cant take others opinion for this. Everyone will trade on the basis of their risk factor. The only advantage in crypto is that it can grow more than 50-75% in a day or drop. But this is the time to buy and hodl so start buying.