New construction homes are almost universally Value of Land + Cost to build structure + ~10%. The supply/demand aspect of new construction cost only factor into the value of the land, and how increased demand can cause increased labor/material costs.

It's not like real estate developers pull numbers out of a hat to determine how much to charge. Most areas will have several major developers in direct competition to attract new home buyers, and if their costs every get out of hand people will just start buying land and managing the build themselves.