How to talk seller down to half price?

[Ryan K.]

I'm working on a deal now for a very challenging property.  There's an old house in very poor condition.  Highest and best use is 25-50 apartment units, and the seller thinks so and has it priced as such.  I have put in significant due diligence and, based on a myriad of reasons, high-density multi-family development on the site will be extremely difficult and very expensive based on the current zoning, the existing water and sewer and, most of all, an out-of-service Union Pacific railroad track.  Based on this research and the obstacles that need to be overcome, in my opinion, it's worth about half of what the guy's asking.

Seller is out of state, I believe he's about retirement age. House is rented out but hasn't seen maintenance of any kind for a few decades. Property has been on the MLS and in the local paper for over 6 months, which, in this red hot market, shows it is overpriced or too challenging.

What is the best strategy to convince a seller to take half of what he's asking?