This is not a good candidate for a master lease!
The only thing you should do with this house is gt an option for as low as possible then try to sell it to someone else, perhaps with a highest bidder sale, so you can make a little profit.
What is the lowest option price you can get? $80,000 would be the right number for cash. You could pay a little more if they would seller finance for a year, with low low payments.
Looks like $80,000 was a really good offer for this property. They should have taken it.
No one can get bank financing for a house in this condition.
So, you’ll need to find a cash buyer or one who has private lenders already lined up.
If you can’t get an option then sell it to someone else, I would not advise doing a master lease on this property.