a few quick questions since I am not in Calif but I kinda know psych/health ins stuff some..
the $300 test.. I don't think you need anything that in-depth (that's about 2 hrs of testing and what I know about the psych letter is they ask you some q's and write up a report about your weight loss attempts, supports, etc etc etc.. it's not a "Psychological Evaluation" per-se (caps intended)
Things to find out/ask about (insurance company or whoever the letter/evaluation is for):
1. What kind of credentials does the evaluator need?
2. What content should the evaluation have?
3. Ask them to send you a list of people who they accept that cover this service (they CAN do that - they should - now how up-to-date and accurate the list might be is another story...)
The $300 test is done by a MD-psychiatrist or a DPsy -doctorate of psychology and I think that might be overkill... You MOST LIKELY (of course I'm speaking from another state) could use anyyyyyyyyy therapist that has a license - such as an LCSW or LPC. My surgical center had a list of people they suggested (not demanded) and one person I know used the therapist they were already seeing. The clinic was able to tell her what the letter needed to entail. I have a therapist but ended up going to the psychologist the center had on site because the evaluation was specific to having surgery, which was needed and not my therapist's specialty (he also wasn't that comfortable about writing a letter for something he knew little about at that time - he has learned more since but that was then

)