Prurisol is lots cheaper to manufacture than a biologic. We don't know what it costs to manufacture Brilacidin and Kevetrin but it would be surprising if it were really expensive. So often with drugs, the gigantically high prices we pay are not related to the cost of manufacture, but to the profit that the piggies want to make. Look at Shkreli raising the price of a cheap drug by 5,000% because his company controlled the supply.

So I wouldn't expect a drug company to give away even 1/100th of a point royalty more than they have to. The fact the the giants Biogen and Pfizer reached a deal in the "low to mid-teens" depending on eventual sales shows us that that's about what a big company is used to paying.