If you are a fulltime trader,I believe you can earn a passive daily income as a day trader. I suggest you to buy at least 3 altcoins in the top 5 list during the dip then observe the movement of the market price as it goes up before selling it.But this kind of trading needs patience and techniques as to when to buy and sell your coins for a better profit.I bet $100 as what you've said is just a little amount so you better choose the promising coins to trade.
You have a point on that mate but I don't think it could say a passive income since we here in crypto currency community as we try to wish our luck here. Also, due to the volatility of different altcoins we can never expect a great outcome but I can assure that it can have a great profit but as what I said not always as you may experience some losses of your investment since we just hoping here.