I don't give them any of that. They ALREADY know what they think it would cost them to get into your space. They figured that out long before they called you and talked to you. That they called you means one of two things; Either the number they came up with was large and so they are looking to see if they can get a discount by buying something, or there are some employees in your company they want for their effort.

This litmus test will tell you which it is. If their number is reasonably high, they know it will be hard to get into your space. If the number is low, they just want to poach employees.

There is zero value in talking to them without a number you like on the table. You must defensively reduce the information asymmetry in any way possible.