Talking about the amount of investment, it really comes back to each individual because he will do it according to his abilities, indeed the monthly amount is quite large and the average standard salary in several countries is indeed not enough for that, but if he has a good position in his job, he will definitely able to do it.
In my view, collecting bitcoins at a total price of $ 20 / day is of course an inappropriate strategy in my opinion, because it will take a lot of transaction fees which are quite hefty if collected, it is better to extend the purchase interval, for example once every 2 weeks or once a month with a total amount the same one.
For example $ 20 X 14 days (two weeks break) = $ 280, and he only makes 2 transactions to make purchases in one month, in my opinion this method is more effective and economical for buying bitcoin.
Someone can do without coercion in their minds to be able to buy at the nominal rate they specify because the direction of urgent needs makes the situation quite complicated for our finances, but we can do it regularly with a different nominal investment rate from week to week.
Previously I thought those who did long term would not be a problem for them if they missed a few buying periods due to financial instability. However, they will resume buying when their finances stabilize.