How expensive is making humans vs. their utility?

Utility for what purpose? If we're talking about say, a paperclip maximizer, then its utility for human beings will be measured in paperclip production.

Is there something markedly more efficient that won't complain or rebel if you treat it poorly? How efficient/useful could a human be if you treated it well?

It won't be as efficient as specialized paperclip-production machines will, for the production of paperclips.

Are you willing to accept that premise and see if you can draw any helpful conclusions or give any helpful advice?

Yes, but you're unlikely to be happy with it: read the sequences, or at least the parts of them that deal with reasoning, the use of words, and inferential distances. (For now at least, you can skip the quantum mechanics, AI, and Fun Theory parts.)

At minimum, this will help you understand LW's standards for basic reasoning, and how much higher a bar they are than what constitutes "reasoning" pretty much anywhere else.

If you're reasoning as well as you say, then the material will be a breeze, and you'll be able to make your arguments in terms that the rest of us can understand. Or, if you're not, then you'll probably learn that along the way.