I agree- hiring an appraiser would be a good place to start. Might be worth the $300 or so in fees.
Also, a Broker Price Opinion- usually runs $75- $100- might be another, cheaper way.
I used to be in RE development, and I'd be happy to take a look at it and what else is around town and let you know what I think. That's not official, but it might help- along with your 2007 town assessment.
Thanks, and good luck,