Someone ask me a question after introducing bitcoin to him, if he can start up with $30 and grow with it but I told him bitcoin is wide and high in volume, price and market, that's means whatever you're starting with determine the outcome of the market like for example; if you start with $30 and eventually the market goes up to a little increase of $32 can not be compared with someone who started same time with you, at the rate $100.
So also when the market is down to some extent, the person with $30 may likely loss more because of the money is small. Blockchain has the minimum amount one can invest if am not mistaken but if your amount is too small may be difficult to make easy progress.
What do you think about my advised to him?
You are correct that crypto currency markets can be very volatile and value of your investment can fluctuate rapidly. However there is no problem with starting investment in Bitcoin with any smaller amount of money, however it is advisable to invest your savings in Bitcoin regularly, in particular when market is in down-trend. This strategy can help you to accumulate more Bitcoin holdings and increase the possibility of generating significant profits in future when market is in on an upswing.