Why is it cheaper to use sheep in an experiment rather than humans

please tell me asap!! late answers will not be considered for best answer

Because in order to use a human, you must first prove your item is safe to the FDA which can cost hundreds of millions of dollars and you must satisfy all the ethical requirements that come with testing on humans, obviously you cannot use anything dangerous on a human.
The sheep is a good analogue because it has the same tissues as we do and can produce alot of the same proteins and it is also a mamal.

umm, maybe because humans expect to be paid and sheep don't ??!!