This doesn't make much sense. In this situation, the party should pay you a good fee to create a library of work for them that they could then use in their materials. If they are just saying they want you to take pictures, some of which they might use and which they will pay you some amount per, that isn't stock, that's just shooting on spec. The whole situation sounds kind of unclear. Do they want exclusive usage? Can you license to the other party? What kind of things do they want you to shoot?
Sounds like you're going to be doing all the work, and more than they need, for not much cash.
