My assumption is the current owner would have a lower replacement cost, so ask your lender and then get your quote from your agent.

She is now, after the last deal she had going fell through, wanting to sell the property to me via owner will carry/lease with option to buy OR assumption of the loan.

Going back to commenting, even if it costs more to build, which I doubt is a correct assumption, new builds always pays more than a rehabbed house, in other states, it might be 4-6k but in CA 30-50k is a normal difference.

When I started investing, I was under the assumption that I wanted to make my realtor a very wealthy person!

You could play it up and further demonstrate your level of seriousness by saying something like: "This offer is based on our assumption that the property contains a mix of 1 and 2 bedroom units totaling 16 rentable units, along with our initial research of publicly available information."

It was packed full of new golden nuggets, corrections to some assumptions, and validations on some recent investment activity.   

Outside influence of family and friends some who do and don't invest have all gave me the assumption it would not be smart for me to invest in yonkers just mainly because of taxes and property price .

What is your assumptions on overhead costs?  

Appreciation assumption?

But my assumption is that even that premium would still be below the inflated prices I'm seeing on the popular websites.