Is it ever okay to experiment on people if they know the risks and the risks are low?

I watched a movie the other day called Extreme Measures.  *movie spoiler alert*  A famous doctor was taking homeless people and performing experiments on them to find a procedure to allow parapalegics to walk again.  The ethical delimna was whether he should sacrifice these few homeless people in order to help thousands of people who are unable to walk.

It made me think about the issue.  Science sacrifices animals all the time to determine if a medicine or medical procedure is safe and can then be used on humans.  The animals cannot be asked if they wish to be part of the experiments.  But humans can.  The doctor in the movie was obviously wrong in using people without their knowledge.  In the movie, he states that he is rather old and doesn't have time to wait years for experiments on rats and monkeys.

Is it ever okay to experiment on people when the odds of survival are slim to none?

Obviously, taking people, homeless or not, is unethical.  But what if you asked for volunteers?  If you spelled everything out to people and showed them the risks and benefits, to them and humanity, would that be okay?  I am of the mind that if people are in control of their mental faculties, they can make any decision they wish.  If someone asks for volunteers and someone steps forward, they can all sign the appropriate paperwork (and maybe be overseen by a 'oversight committee') then the doctor and volunteer can proceed.  I can imagine there would be a few people who would want to do this.  There are always a few individuals who will volunteer for anything.  But would they get the right kind of people?  Would they get volunteers who fit the criteria they needed?

But what if they can't get enough volunteers?  Maybe the odds of success are too low.  Would it be okay to pay for volunteers?  If people were offered a substantial amount of money, would it be appropriate?  I can certainly see more volunteers stepping forward.  Money can be a strong motivator.  And even if the odds of success are low, the money could be given to their family.  If the volunteer was of sound mind, would this be okay?

I am of the opinion, that if someone is capable of making decisions for themselves, then they can volunteer for any and all procedures that are offered.  But money should probably not enter the equation (maybe living expenses?).  It makes the reasons for volunteering more difficult to ascertain.  And I like the idea of an oversight committee.  A group of medical professionals (and laypersons?) who make sure that what the scientist/doctor is doing needs volunteers and that the volunteers are not being coerced.

The needs of the many outweight the needs of the few, or the one.  As long as that one understands the risks involved.