1. You need a door with U-factor below .3. You can either choose to use the door from Western (and they are a high end quality manufacturer), or else you find another company with a door that meets Title 24 requirements.

Since these kind of doors are probably more popular in California than elsewhere, and since a number of the major manufacturers of these doors are located in or close to California, I am surprised that you haven't been able to find more than one company that meets the requirements.

2. Not sure where you researched to conclude that a lift and slide or accordian door would be about 1k/ft. Realistically, at least in my experience, somewhere between 1.5-3k/ft really is more realistic. And as you said, not including structural upgrades to your home.

Haven’t been able to find much else besides western that isn’t astronomical. There are tons of I use wood or vinyl, I’m strictly speaking about aluminum or clad with spacer. I think most people get around the u factor by bundling in other work that is energy efficient.

I’d minimum starting prices at 1k per foot. Any structual/ framing cost are merely a guess since every house is different and there can also be mechanical issues as well. I am not sure you get around the U-factors and solar heat gain requirements by bundling things together. Preferrably You are seeking out a contractor that is suppling the door and installation and better yet the framing as well , but may be difficult. A good door installer will know all the rules and should be anle to answer all these questions for you.