お金

How it works

が (subject) marks the subject — the thing there isn't enough of, here お金(おかね) (money). The verb 足りる(たりる) (be enough) shifts to its plain negative 足りない(たりない) (not enough), so this is casual, with no polite です (is) or ます (polite) at the end. Literally it says “money isn't enough” rather than “I don't have enough money”.