It varies quite a bit! It also heavily depends on whether you're hiring a WGA writer or a non-union writer. However, a good rule to keep in mind is that writers are usually paid 2-5% of the budget for a feature film. So if you were making a $1,000,000 feature film, the writer would on average be paid $20,000-$50,000. Hope this was helpful!
For this specific project, it wasn't necessarily a consideration. Our client wanted to tell his own, unique story, which lent itself to creating an entirely new IP. Furthermore, acquiring an IP was also out of our budget, which also drove us to creating something new. However, that is not to say that acquiring an IP is not a viable option, but in our case, it wasn't the most cost-effective or logical option. We hope this helps!