I think if a person is interested in Bitcoin investment and he has only 30$ then best option will be that he should use these money to get some experience in trading rather than expecting huge profit from them. Because profit from Bitcoin investment depends on how much amount you invest and how much percent Bitcoin price goes bullish, if you invest 30$ and Bitcoin price goes 10% the you will get just ten percent which will be 3$.
So when ever he got some big fund from different source then you should welcomed him in really world of trading where he can expect some bit from his investment..
Of course, if he makes only $3 profit, that probably won't even cover the fees for buying and selling bitcoins, but he will still make a profit. And learning to trade from scratch with $30 will most likely result in him losing the entire $30 altogether. I can quite possible to advise him to buy bitcoins, especially in a downturn, but I personally would not dare to advise anyone to start trading, the risk is too high.