The DCA amount does not need to be the same amount, and the DCA amount and the regularity of such investments could strictly be based upon when a person has a certain level of discretionary income that is upon his own choosing in regards to reaching such thresholds, so even relatively modest amounts of investing into bitcoin could end up paying off quite well in the long term, as long as the investor also understands that investing can sometimes take time to play out.
I really feel there should be a base amount when DCAing, sort of an amount you should not go below, so as to put yourself in check and foster continued discipline and commitment in your investment. This comes from the knowledge that the human mind is cunny and can overly adapt to a pattern and possibly exploit it to the disadvantage of the individual, so for example, If you set a base, lets say $50 and you know that you can afford it weekly as a minimum, at some times when you have more cash with you you can invest $70, $100 or even more provided you have made accurate plans for the next week's minimum of $50 to fall in place. you are better off than someone who invests $200 this week and possibly $20 next week, $30 in two weeks time as he can even decide not to invest in a week citing and deceiving himself that he has invested much previously.
This will help you become more disciplined and consistent investor over a long period of time as against investing randomly without an investment guideline for yourself and the guidelines would help you succeed in your investment journey with ease as it tends to be part of you overtime and as a committed investor, the more your earnings increase, the more you raise the bar on your minimum investment and the more bitcoin you would accumulate over a long period of time.
Of course, it is good to assign a fixed amount from our discretionary income into regular buying of bitcoin through DCA weekly or monthly but sometimes this might not be possible because it is not of our own control but based on our expenses that arises in different weeks. If you observe sometimes we might spend more than what we budget for the week due to increase in our needs for that week and sometimes we might spend less due to decrease in our weekly expenses.
In such scenarios the investor might choose to invest $50 weekly but when the expenses of his needs increases, he can cut down his DCA amount to $40 for that week and if his expenses on another week decreases, he might increase his DCA amount to $60. The most important thing is that the investor did not stop buying but continues buying no matter how small he could buy in a week.
Also an investor might have an increament in his monthly income, or has an additional means of income along the line of his bitcoin accumulation journey, he will increase the amount that he is using to DCA in order for him to buy bitcoin more aggressively as long as he did not over do it.
There can also be a case where an investor did not have any discretionary income on that week because of too much responsibility for the week and his discretionary income was exhausted, such investor don't need to worry that he did not buy bitcoin for that week and he will just hodli and buy the next week. Another scenario is if the investor loses his job at that moment, he is to pause his bitcoin accumulation until he gets a new job while he feeds with his emergency funds and reserve for the main time till he gets a new job and continue accumulating. If you have the funds to keep on buying don't stop just keep on buying.
Nice instances you've go there, but in my own reasoning, the only scenario that has to actively affect the investor's accumulation journey for a period of time is when the investor looses his source of livelihood, then he might take a temporal break until he gains his ground and resumes his accumulation journey.
Addressing that of when the investor has a lot of expenses or was not able to buy at the base price as @Sticky Bomb illustrates, the best thing is to buy as much as he can for that week and note down the makeup amount and roll it over to the next week or thereabout, maybe he was able to buy $30 worth of bitcoin for this week, then in his accumulation record book, he should push the balance to the next week indicating a purchase of $70 to offset the previous week if he is still able to maintain that base price, where he cannot, he should be adjust the base amount to any amount he is comfortable with. the most important thing is to set standards and follow suit to maintain discipline and consistency in the accumulation journey. Base price is a rule and can be amended to suit the investor's capacities.
The most Important thing is that he does not stop buying, remains disciplined, committed and accountable to himself and does not leave his accumulation journey to chances but follows some standards set by him to guide him in the accumulation journey. It is good to always know what you are expecting from yourself and it will motivate you to do even more than average, there is a saying that if you aim for the moon, even if you are falling, you fall among the stars meaning that worse comes to worse, he settles for the base price.