WARNING - With the above mentioned stamped design fee's none of you try to set up shop here in California.
Example in Los Angeles area: a simple single story 800 SF room addition is between $1,500. to $3,000. and it is not uncommon that we pay $4,500. to $7,000. for design/structural on a 1,500 SF house remodel that has some structural up grades, oh then we need "Structural Observation" at typically $300.-$400. each and "Deputy Inspection" that runs $200.-$300. a pop (epoxy inserts, welding, etc.).
When I try to explain why a 2,500 SF house cost between $165. to $225. SF to customers they usually don't get it. And the above does not include plan check and building permit fees ($7,000. to $12,000.) and impact fees, connection fees, school fees, on and on that cost $15,000. to $60,000. per house.
The flip side is that this house value, in a decent market and in a decent area, has a sale value of $425. to $600. per SF or 2,500 SF @ $500./SF = $1,250,000.