Thanks for your replies so far. I have the lot in the middle of the assembly, and the two on the ends are rental properties, so those owners will be a little more willing to sell. I'll check out the expropriation compensation model, if I can find it. :)

I've got a realtor quite interested in purchasing my 35' lot in the inner city, along with 3 adjacent lots to build a 3 or 4 story residential building. Any guesses on how much (if any) extra I can ask for it, considering the assembly opportunity and the increased FAR?