Waiting and piling up the cash in fiat before you buy is totally the wrong approach if you ask me because Bitcoin isn't a stable coins and you can't expect the price to sit around and wait for you to gather all the money first before you now use when you are satisfied with the money for investment. The right thing to do is simply to keep striving to accumulate just like you have stated with the little earning so that you can meet up with atleast the lower price because you can't tell when the price might go up or even down.
I have thought about doing this, with the income I have every month I will set aside some money to save and invest, of course not forgetting to meet my needs. Indeed, if you wait for the money to accumulate and then allocate it to Bitcoin, that's possible, but I don't think everyone can hold cash in fiat consistently, because there are unexpected needs or expenses and the money in the pile will always be used.
Of course, we won't know whether the price will rise or fall in the future, but what is clear is that we hope for the best, namely that the price will rise.
Exactly fiat cannot be held for long without an unforeseen force will come up and eat it up. It is good that you have an income in which you are planning to use some fraction of it to start investing in bitcoin. What you should do is that you don't need to wait till you receive the money before planning since it is certain and a guarantee that you will get paid. It is better that you start a rough work on your monthly expenses and needs so that any left over that is what you can use part of it to invest in bitcoin for a long-term. While you use the other part to start building your emergency funds to that of three months at least, before you build your reserve funds. The reason why is because so that you can continue using that amount to invest weekly or monthly regularly consistently amd persistently in order to build your bitcoin stash nonstop.
It is better to prepare down so that immediately you get paid you get started immediately. There is no time, as the price of bitcoin is unpredictable and you have no bitcoin yet so delay is dangerous because we do not know what will be the price of bitcoin next. It is good that you use the DCA method only for a start so that it will enable you to stay focus in accumulating regularly and also reduce tension since you have assigned the money to investing on bitcoin.