You do not owe an identical answer to requests that cost you different amounts.

Consistency is a decent instinct that goes strange when applied to costs rather than to people. Two requests can look identical from outside and cost you an evening and a fortnight, depending on distance, money, health, and whatever else the week already holds. Answering both the same way in the name of fairness lets the cheap one set the price of the expensive one. Fair treatment is not the same as an identical answer.

When you feel obliged to match a previous yes, work out what this one actually costs you. Say the difference briefly if that helps, then answer the real question rather than the precedent.