Actually if $50 is your budget for a mic. for a school project, I would suggest you do not use sound at all and make a silent movie.
Any sound will be total cr*p, so make a silent movie.
This will actually concentrate you to make the pictures that will tell the story without sound and you will actually learn a lot about picture making by doing it this way.
Only do sound when you can get the equipment to do it justice.
I'm not talking top of the range, just enough so that your project will be worth doing and not destroyed through bad sound.
I don't know how many times I've stated this before and here it is again.
I've used 5d mk2's internal mic and it was okay. Others are using their cellphones and P&S cameras and it's okay. Would that $50 mic be worse than those? You know the answer.
This is a simple school project; not a broadcast material and speakers in the classroom already are el-cheapo POS to begin with.