Ask HN: Negotiating with my boss to take on project about to be outsourced?

The company I work for is developing two nearly identical products with a single fixed deadline. We are currently working on the more complex product, and plan to make the necessary changes for the other product near the end of the project. The feature sets are similar enough that the changes are exclusively policy, instead of mechanism, and are just busy work.

Concerned with the limited time remaining until the deadline, management is considering outsourcing the lesser product to a consulting firm. You know, nine women making a baby in one month. But this will require a lot of support to get this other company up to speed, and through out the remainder of the project. Additionally, this will create two parallel codebases to maintain in the future.

How should I, as a salaried employee, negotiate to take on this project for a substantial bonus? I am the only developer in the company that can work across the entire stack involved, and I have proven both my competence and value.

I'm considering countering the consulting firm's offer (currently unknown) at 66%. I know I can clearly lay out all of the advantages of keeping this in house, but what is my leverage? What is stopping them from keeping it in house, and giving me no additional compensation? This will require significant overtime on my part, but like I said, I'm a salaried employee.