Listing Subject To ?????

[Tony Wallis]

Heard Pace Morby (he was great) on BP Podcast the other day and sparked this question. I have a listing coming soon, was a rental for last 4 years, and the owner is out of state and is not an investor. Rented it becasue he could not sell in 2017. Did not screen and got bad tentants. Tenants are out but left a mess. House has big upside with ARV around $325K. Seller wants out but to sell as is, we would be very lucky to get $250K which is his number, if he gets close to that, he is happy. He does not have funds to do any rehab and is concerned about paying 2 mortgages. Thinking about doing a "subject to" agreement where seller gets 250 or lower if we can negotiate when we close. We pay mortgage (2k) for a month or 2 max while we do renovations.
Needs paint, new kitchen, roof. Roughly 35K (includes 15% buffer) Identical house 4 doors down sold for 325k with multiple offers 4 months ago. Looking for thoughts on structuring the deal.