I have never seen a $125 per square foot addition in Southern California in over 30 years. The labor would have to be free slave labor or sweat equity for that to happen! Prices for average homes start at $185 per square foot and go into the $800's and above for luxury homes. Your project should run in the approximately $220 +/- range, but only detailed plans and fixed material and labor costs will determine your project cost.
Hire a general contractor capable of doing a design build to estimate your project or start with a detailed set of desires to give an architect. Your design build estimate should be faster, but an architect will often give you aesthetically pleasing designs you wouldn't think of otherwise.
When you hear of price per square foot people often calculate only the build costs. There are many fees, permits, delivery costs, etc. that bring a project value up - easily up!
Rory Burchatz, Owner
Building and Construction Contractors
CA Lic: 759677
P: (714) 892-0428 F: (714) 892-0105