Been a while since I worked on anything Taxi related but I just got a cool offer today that might bring me back to producing for this kind of business !

So one of the libraries that got a lot of my tracks are offering me an advance fee to produce new tracks. In the past it was just a "we pay you if we sync the track" kind of deal but now they offer to pay an advance fee then exclusive rights on it.
What would be the ball park price for one track ? Or like a bundle of 20+ tracks ? Considering, from my understanding, that it would be the only time I would get paid, the tracks would then be theirs 100%.
Please let me know, maybe in private if you don't want your prices to be public

Mathieu