@Allan Smith @Josh Braun thanks for the replies. Useful to know.
The average price per sq ft for the end purchase price on some of these I recently analyzed was $262. So for a 2,000 sq ft house that is $524,000. If a builder can place two of these on the existing lot the end sales price would be $1,048,000.
However, this formula seems to break down a bit if the sq ft of the new home goes up. If the builder is building two homes at 2,500 sq ft or 3,000 sq ft this drastically changes the final purchase price of the land.
For example, with two 2,000 sq ft homes at 23% the land would be worth $241,040. However if the two homes are both 2,500 sq ft then the land would be worth $301,300 at 23% (retail value of $1,310,000). You see the problem with this formula? I guess the best way to find out is to contact builders and ask what they are willing to pay? I am planning on calling a bunch on Monday to see if I can get a better idea of land values. I have 3 leads in this area and am unsure what to offer the sellers without a better picture. Thanks again for the responses. Really appreciate it.