What should someone who vowed to donate money or a sheep in Ramadan if they got a job do, given they didn't fulfill it because Ramadan began and they are experiencing financial hardship?

This conditional vow is disliked (makrooh), but fulfilling it becomes obligatory if the condition is met. So, if the man is granted the job, he must fulfill his vow, whether it is through charity or sacrificing an animal. If he is unable to fulfill it, he must do so whenever he becomes able. It is more prudent to offer an expiation for delaying the fulfillment.