How much to Charge for VR software?

I have developed a VR app using unity to demonstrate how to winch a vehicle (apache helicopter) into a cargo aircraft. I was casually asked to do this by a friend working for an aviation teaching business. It uses high quality graphics and the real world physics of unity.

They have now asked to go into negotiations for it but I have no idea how much it is worth? It has all the functionality they want (attaching a winch cable to a vehicle in different configurations to winch into the aircraft). The aircraft model is scaled accurately.

But what is it worth? 🤔 I have literally no idea.

Appreciate any help 🙏