A lot of people on this forum post replies having never experienced an international medical experience. Let me give you some real answers to your questions.
I spent 5 months in Honduras working in a medical clinic my year following college and before medical school. Having no medical training, there is still a tremendous amount of good that can be done. People don't realize the amount of need and compassion that is lacking in countries like Honduras, and no--there is not enough help to do everything. While there, I learned to take patients histories and do physical exams (fluent in spanish helps), and by the second month was seeing patients on my own and presenting to the attending. Considering we had to see 70 patient/day with one physician, it helps tremendously to have pre-meds or medical students to see patients and triage cases. Furthermore, assistance with procedures and other aspects of medicine like wound care, that a nurse would usually perform, can easily be performed by pre-meds who are properly taught. The cliche "see one, do one, teach one" is very applicable. The experience will put you closer to patients than most have ever experienced or thought was possible as a pre-med.
My experience was an amazing one and one that I will always remember. It will provide for the student a whole different understanding of compassionate medical care and in my case changed me as a person.
The cost issue is one that although the money would be better spent sending it to a NGO, in all honesty, I believe it is better spent on the experience, and let me tell you why. Not only will the person undoubtedly come back as a doctor, in my opinion, Think of it this way: aside from your flight, the remaining $1000 is all contributing to growth of that country. Every cent will be spent there, with a portion going towards the clinic or other operational cost. These organizations on most accounts use the money very well and waste little.
If you are at all considering the experience, do it! But remember, it is very tough going to a country where no one speaks english and trying to have an amazing experience. Learning some spanish before you go will improve your experience tremendously and you will feel a much greater impact just being able to talk to your patients.