Fred, you can hire a real estate agent on a flat fee basis to do a market analysis. It's pretty quick and dirty, but it would be a real professional's judgment of value, which is a lot better than any of us lay people poking around to find comps and making our best guess. Since money is tight (it always is) you can save by hiring that same real estate agent to handle your closing rather than an attorney. I'll be if you checked, you could get a competent and experience real estate agent to give you a market valuation and put together the closing papers cheaper than you could have a lawyer do just the closing papers.

Also, what's the tax assessed value? For commercial property it should be pretty accurate because the county wants to maximize value/tax revenue and commercial property owners want to minimize their tax liability, so the give and take between the parties often ends up as a good reflection of market value.

It is really hard to value undeveloped commercial land. Don't rely on Zillow (unless it supports your offer price, of course). The vagaries of what makes raw land valuable or not are almost infinite. At least talk to a real estate agent. You won't pay a commission since you've already located the property and are just negotiating with the seller. If the agent gets paid it will be on a flat fee basis for providing a specific service, so don't be afraid to contact a real estate professional.