If I were to assume that all human lives had equal utility, I'd press the button, many times. But I don't think that lives-saved is a very good utility metric. If a person is saved from, say, malaria and malnutrition, and then grows up poor and uneducated and becomes a subsistence farmer, contracts HIV and dies, leaving behind several starving children, I am completely unabashed about assigning a lower utility to their life than someone living in healthier circumstances.

As the scenario is formulated, I don't think there's enough money to make me confident that the scales tip in favor of pressing it. But I'd do it for more money, or a guarantee that the person dying would be in similarly poor circumstances to the people being helped by the charities.