Using the expression extra cash, left over cash, or discretionary income would have been more better than using excess money in your expression which sounds more ambiguous to me, it sounds more like one needs more than enough prior to starting bitcon investment since anyone can come in with as little as what can be called left over money when our basic needs has been taken care of.
With DCA of course buying every week will be better, so discretionary income will be more appropriate to be used to buy bitcoin. Someone will be able to apply the DCA method if they are good at managing finances, meaning if after they divide their finances for living expenses, daily expenses and after they add up until there are a few percent left or it is worthy of being called discretionary income then they can use it to invest in bitcoin.
Especially for newbies, of course they can take a stance to start it more consistently if they start it at the beginning of the year. Investing in bitcoin must be in their self-reliance because bitcoin investment is not free from the word risk as expressed by JJG.
apart from that. Starting an investment only requires a mentality and willingness to change fate by investing in bitcoin. In investing in bitcoin, people often panic because they are not mentally strong, therefore the choice to hold for the long term is more recommended and do not consider price movements in the near future because the investment target is done for the long term.
Budgets certainly vary and depend on each person's discretionary income, some start with $10 a week and some buy $100 a week. For that, focus is something that must be in us to accumulate bitcoin at every stage in the plan that we have prepared in investing in bitcoin