Cost of square Footage for House Building
This is probably the best real estate question, asked by customers and amongst real estate professionals. I have interviewed many builders, investors, general contractors and never is there a one amount fits all answer. Everyone is correct. As noted in other responses - site work and engineering may add expense. A form A lot, engineered and private sewerage and well (if applicable) will run at a higher premium than raw land. If you consider a builders package where the builder owns the subdivision - those costs will be masked in with new construction costs.
I suggest taking a trip to a 'box' store and browse the prices of materials, including kitchen and bath complete packages. The large price variations for a single component e.g. roof, the bargain shingles vs. lifetime warranty high end shingle can double the cost. Kitchen cabinets - use per linear foot can be triple depending on the craftsmanship.
Another good measurement of costs is modular home construction. I have visited several modular home companies and also their assembly plant. The pricing is fairly straightforward and can be a great source for price comparisons. You will be able to see the cost of upgrades for kitchen, bath, flooring, windows, electrical fixtures, doors and windows is not dissimilar to 'options' or 'trim packages' on a car. The quality of materials will stand out. Labor for installation will remain the constant low end to high end.
In the end, the more you know the better consumer you will become.
California and the Southwest has large home construction companies. They achieve savings in volume of new builds, but the individual general contractor may offer cost reductions with modifications to the house plans.