What are you trying to achieve? Are the characters block like? Are they cartoon-like? Are they photo-realistic? How complex is the animation? Is it just rigid movements? Is the rapping going the be jaws moving without any synchronization to words or will there be synchronization? If its all of the low-medium to medium and high quality, then I doubt anyone is going to do it for $50 given the complexity.

It would be far easier to hire a camera and just film it with actors and props. Much more realistic than what 3D is going to result for the same price. I think project like this done commercially will cost a few thousand dollars at the very least.