You should have a minimum of $ 500 to start trading. Because too little of this you will not have much profit, and you should choose the big floor like Binance, HitBTC, Bittrex ...
Minimum amount to start trading should be based on our own financial condition. We should not force ourselves to use the same amount suggested by others because $500 can be so big amount for others as well as can be so small for some other people. We know our own limit, in the beginning of trading we should think more about learning than think about gaining profit.