Over $6000 to install TTI headers on 66 Barracuda

I know the cost-of-living is high in Silicon Valley, but that is crazy. Sounds like his fault for lack of communication. There should have been a written estimate. If not, he is one hanging in the wind. CA has pretty strict laws to protect consumers for auto repair. I complained about a shop once and they actually called me back and investigated. Try that. After that, there is always small claims court.

Rule of thumb for most work - auto, home, whatever, is that labor costs are about equal to parts cost. Of course, not true if replacing a $5 clutch throw-out bearing, but usually true for high-end bolt on parts like your TTI headers.