It is better you invest low amount of money on bitcoin right now. If your salary is $400 monthly, you can be investing like $20 on bitcoin which is 5% of your monthly income . The price is high already but there is tendency that the price might go up. If you can be patient, wait until the next bull market begins after the coming bear market to invest more. I may not be absolutely right but that is my opinion.
You are actually right mate, this is same thing I keep telling anyone who might be fascinated by the bullish momentum of BTC and wants to jump in now and buy. The price is currently high and of we remember correctly, we are only supposed to buy low and sell high. There's actually a risk right now in buying Bitcoin at a high price as it might drop and your investment would take longer to get back into profits.. it's better for op here to invest little like you said and wait for the next bear season to arrive.
If they are not sure but still want to try just to start up their journey then spending small amount to start is nicest thing they could able to do. Bitcoin is strong currency though and provably that their money is safe there especially if they look forward to sell it for long term purposes. But if they just aiming to buy and sell low then maybe they would struggle to find good position especially if they are using small amount since provably the current volatility of bitcoin might confuse them and provably this would leave up to more higher risk to lose their money.
But if they are not really so sure about their decision to invest with bitcoin best if they listen to their doubts and just start to gather more information then invest if they are truly ready to take the risk and apply those things they learn.