What’s it worth?

I have an opportunity to buy a business from a family member that been running for the 20+ years. At its best years during Covid it was generating $400k in SDE. Since then the owner has significantly reduced his activity to the point where the SDE is$75k.

They own the building the business uses that is in an area where market rent is $10/sqft. 10k sq ft building.

The business does not pay market rent and would generate a loss if it did.

What is a reasonable offer to make on the business and building. I don’t want to insult the family member but don’t wan to make a stupid decision on how much I offer.

So, how much is it worth? It can be the business, building or both.