From a small piece to go around an incandescent bulb, to expensive LED tilting "eye ball" trim.  

I know it's an  impossible question to answer correctly, but if you had to ball park it how much?

Now if you put a ball down and it starts to roll fast somewhere, then that is serious settlement and probably needs a new beam or something jacked up. 

Later after you have renovated and stabilized the property you can refinance out if you need to.Otherwise you will need to find a Hard/Private Money Lender to start the ball rolling.On a side note.  

The house needs a lot of work, but seems structurally sound with no signs of any major interior damage (mold/water/structural issues)- Is there a way to get a ball park estimate for what this house would need prior to contacting a contractor?

Get as much as you can, as long as you make a profit. yes, if the neighboring property sold for a certain amount per square foot then yours should be worth at least that. but you know he is trying to put a land puzzle together for a bigger development, so the ball is in your court. are you going to hold on to the property forever to see if the value does go up ?

I would check with your lenders "Crystal Ball" to see what he has to say.If you want to run the deal by me off line let me know.Good Investing.

I may just go the easy route and low-ball and see what interest I get in return.  

Contractors by themselves are not necessarily reliable as they may low ball the numbers in the hope of getting some work with you.

NASB with Jason Zook had an appraiser who low-balled my appraisal by using a city about 20 miles away as comps on a quad plex cuz nothing sold within 6 months in my city, instead of using comps from 12 months ago.