Subdividing 1 lot into 19... How to value pre/post? 🤔

[Steven E.]

My wife and I are subdividing a single, 5-acre plot of land in Riverside, CA into 19 individual lots.  The goal is to eventually build residential housing on them.  We have been working with a civil engineering firm to prepare the soils reports, assess zoning, etc, etc and a RE attorney. Both are in preparation for the first value-add step of subdividing the land.

We are told that, once subdivided and recorded with the city, the total value of the 19 lots will be much greater than the value of the single, undivided lot.  It will also allow us to sell off one or more lots if desired, to finance the next steps of engineering in prep for construction.

There is a cost to subdividing, so we are trying to think about the return on our money.  How does one go about estimating the difference in lot value, pre and post subdividing?

For the single lot - presumably an appraiser would value the land using comps?  How much would an appraisal cost and who would we reach out to?  Are offers to purchase the land (we have a few) also a way to think about value?

For the subdivided property (19 lots) - similar process as for single lot, i.e work with an appraiser who will use comps of similar lot size in the area?