I hope this message finds you well. I am a licensed attorney with over a decade of experience dealing with contractual negotiations relative to issues just like this one. Moreover, I am also a licensed IP attorney and deal with issues that are similar in contractual processes as well. It is a pleasure to assist you today.
The short answer is that as long as you are not misrepresenting the costs to the buyer (i.e., telling them they are paying for one thing when it actuality they are paying something different), then you are fine. You cannot defraud someone into believing the raw cost is something that it is not. However, you are bundling a service and can charge a single amount for that service and be fine.
They can demand to see what was paid to the animators only through subpoena. They can only subpoena you if they file a law suit against you.
Your negotiation skills reduced the cost of the animation. You certainly do not want a cost breakdown to reflect anything more than what the animators are charging for their service in an itemized breakdown. However, if you are giving them a single cost for production that includes all services in one, then you are not committing fraud and will be fine.
Let me know if you have any other questions or comments. Please also rate my answer positively (three or more stars) so I can receive credit for my work.
Best wishes going forward!