No, I would suggest they contact USC admissions and tell them that they simply cannot afford to attend. There is already a stipend for air (I recall it was $60 for CA, and up to $200 for other states), and it is possible that with documented extreme financial need there could be additional help or the possibility of an alternate interview plan. It is always worth it to ask.
When money is an issue, the student may have to travel alone and take a red-eye so they spend only the night in the dorm and do not need a hotel.
Another reason I feel it is worth it for a high-need student to attend the scholarship interview is that the student has EARNED a scholarship interview for an incredibly prestigious scholarship to a highly selective university. They deserve the woo-fest of being courted by USC and experiencing the scholarship Explore. They will not be the same afterward. Whether they choose USC or not, it will have an impact on their self-image for the rest of their lives that a need-based package will not.