The night phase is a budgeting problem wearing a horror game's clothes. You have three ways to act during Tsumimi's stream and a limited amount of money. Spend it in the wrong place on the wrong night and the ending you were building never assembles.
The choice text and the cost are shown together, and both are part of the decision. A single Mega Chat can be a specific amount - a walkthrough-level route has been documented where a $1500 Mega Chat on Day 1 and a $2000 Mega Chat on Day 2 each gate specific outcomes - so the price tags are not decorative.
The game asks plainly: "How will you use your limited funds?" There is not enough money to do everything you want, which means every night is a triage decision - which intervention is worth the price this time, and what are you giving up by choosing it?
Because a late-night gift can change the next day, spending is not only about the current stream. A gift you make on Day 3 may be the reason a Day 4 search returns something at all. Treating each night as isolated is the most common way to run out of money and still not have the clues.
The game explicitly asks "When will you stay silent?" Not every moment is one where you should speak. Letting a stream run without intervening has consequences of its own, and in a game about a viewer watching someone they care about, watching and doing nothing is a position rather than an absence.
Two practical mechanics that make replaying far less painful:
Every night is a contribution to the file. The deductions you can make by the end are a function of which clues you gathered and which interventions you paid for - and because the last two endings only resolve after you wake up, the final night is not the final moment. The ending arrives the morning after.