Your tax bill is 4x bigger than seller's accurate T12 numbers.To summarize, the seller numbers are really only useful for a very back of the napkin analysis.

"Contractors" working out of the back of their truck, writing estimates on napkins, taking 50% up front deposits.

Just do napkin math and figure out what your max payment can be and then you can tell your loan officer what that max payment should be and they will do the math on the max loan amount. 

If you are doing an extremely light rehab you might be in the $15-30/SF, cosemtic rehab might be from $40-60/SF and a full rehab of interior only might be north of $80/sf - There are SOOO many different variables that these should just be used for back of the napkin calculations to verify if a deal is even worth looking into more.Happy to hop on call and talk in way more detail about renovation cost! 

But I need to model it out more than just my napkin math.

It's a popular rule that a lot of investors go by as a back of the napkin rule of thumb on whether something would typically make sense as a cash flowing asset or not! 

We are riding from cap 9 market to cap 3 market, everyone in BP that invested in 2009 is rich enough lol.Now................ the difference is the effect of asset when financed with short term debt vs very long term debt.With very long term debt like residential we have reduced appreciation rate in different market (from -2 to 6% market)to a collapsed of valuation (in CRE using short-term floating) with (DE-)appreciation from -10 to -30%( one 100 bps changes in spread causing a decline of valuation to 10-15% and/or 10-15 DSCR from my napkin calculator ).

In fact they are already breaking the lease since there’s a clause about maintaining it in a sanitary condition and this is decidedly not sanitary. 

Doing some back of the napkin math and listings on Redfin right now it doesn’t look like anything listed right now makes sense from an investment perspective.

I I am playing with different scenarios and want a back of the napkin number I will use https://www.omnicalculator.com/collections/real-estate.