LOL, it is you who was being unreasonable, offering him only 200k for the optionality to tear down and build multi-unit. You low-balled him, he high-balled you. That's how it works. The time when negotiations are complete is when both parties are in equal state of pain.A couple years ago I met a guy that had a cottage (worth $800k) on a 10k sq ft lot. He wasn't looking to sell at the time, but was renting the place. Found out the property was zoned multi-residential so I decided to offer him $1M, thinking he would jump at the chance. He countered with $3.5M. He wanted the price as if the new multi-units were already built on the property and ready to sell.
Location, location, location, everything else is just noise used for bargaining chips.