Lot pricing

[Arcinio Arauz]

A lady I'm working with just lost one of her rentals in a fire. She decided not to fix the home and just take the insurance money to pay off her note. She asked if I would like to buy her lot with the fire damaged home. I said yes, but I'm not sure what or how to determine the price. Then she pulls out the tax bill where it says "land value" and it shows 30K. Really, 30K for a burnt house needing a full repair in the sum of around 75K-100K? She as well as I wasn't sure if that's where we would start the pricing to flip to a rehabber. Homes on the street ARV for 120K-140K.
So my question is... what's the best way to determine a price just for the lot with the burnt house?