I tend to use the real estate tax appraisal from the tax assessor office.  I then use the pro-rata from the building and improvements and apply that to the new price.  For example, if I have a client who just spent a million dollars on a property, and the appraisal shows about 40% is land, then I record land at 400,000.

I honestly never thought to ask for the appraisal.  I will have to make it a point of doing that going forward.