How to value commercial lots?

[Toben B.]

Hello,

We bought up several commercial lots next to our building several years ago and have received an offer from someone who is described on the internet as a builder. They sent us an offer with a 7 day expiration on it, which I know is a tactic to try to get a quick deal. They attached a 1 page appraisal which compares it to a few residential lots. 

Although I know how to do a rough value on apartments and houses, I need a guide on how to value commercial lots. We have about 2 acres with a single family home on it. The value is really in the land. 

This is one of the larger empty commercial lots very close to a highway, but just behind the main street. 

Prior to hiring an appraiser, how do I get a rough estimate of value?