Seller won't disclose replacement cost! Any way to find out?

[Jonn Vidal]

Seller bought house decade ago. 

House burned down recently fully; lot cleared.

Is asking round same price now for just the lot, says insurance reimbursed for replacement, but hasn't answered  how much was the replacement cost, which is needed for the rebuild paperwork as planning dept only permit similar replacement.

What else should I require in the offer, or just walk?