I am thinking you hold the trump card(s) here, so don't fold to the pressure. Milk every last dollar out of the developer. They can afford to give you your riches and still turn a nice profit. They just flexing their muscle in hopes you just cave.
I agree generally, but finding the magic number is hard to do. The offer they gave me was reasonable, but it doesn't seem worth the move. There is tremendous growth in the area, so the amount they gave me wouldn't even allow me to replace the house I live in right now.
Does 150% seem reasonable? This is totally outside of my knowledge base. Never dealt with commercial real estate.
My guess is 150-200% of market value of similar home seems right, but you can't exactly goto zillow and figure it out.
My cousin's husband used to do commercial deals, want to ask him, but they are busy, and not sure he even likes me.