All they need is discretionary funds.. which means that it is funds that are extra after they have accounted for their expenses.
The only difference with my use of the term "income" is to suggest that there is a steady flow of discretionary income every week or every month, and in order to invest into bitcoin you do not need a steady flow of income.
As far as I can understand from your post, the mistake we often make is that we consider discretionary income in investment, but if we look deeply into the matter, we can see that there is a slight difference that would be discretionary fund. By discretionary income we mean the income that a person receives consistently like weekly or monthly. But when we say discretionary fund, it is an amount after spending all expanses. It can be 10 dollars or 20, any number, and in the case of investing in Bitcoin, we can invest that amount. Discretionary funds can be said to be money that I have no obligation to use. I can spend it wherever I want, according to my wishes, and that money is worthy for Bitcoin investment.