Assessing the value of a development project

[Nick Luongo]

I am working with a seller on a unique property in Somerville / Cambridge, MA line in a very hot area and am wondering the best way to attack this. Basically its 3 small abutting lots (1 residential, 1 mixed, 1 commercial). I can easily gauge the value based on its current usage, however anyone that buys is likely going to knock it all down and build condos. I want to bring in a RE developer to take zoning into account and value it based on that, however the seller probably won't trust their value because they'll have a vested interest in the property. The other option is to bring in an appraiser (which I've been told with run 3 to 5k for something like this). Can anyone provide any insights on this and how to get the seller the most for the property? Thanks