Thank you for your comment.
First, 過ごす has several meanings: it can indeed have the meaning of “exceed”, but in this sentence the meaning is “spend” not “exceed” .
毎月3万円で過ごす – I live with 30,000 yens every month. (I spend less than this.)
毎月3万円で過ごせない – I can’t live with 30,000 yens a month. (I will spend more.)
So since 毎月3万円で過ごす means “I live with 30,000 yens a month”, you turn this into the imperative form with ~なければならい and you get:
毎月3万円で過ごさなけらばならい – I have to live with 30,000 yens a month.
Hope this helps.
]]>I have one question though. In the passage above you have the sentence, “過ごさなければならない”. I thought this sentence means “must exceed”, am I correct?
過ごす (to exceed)
過ごさない (not exceed)
過ごさなければ (if don’t exceed)
過ごさなければならない (can’t afford not to exceed / must exceed)