$300 of that price is name only. If you want to spend big bucks on a kickass action, get a BAT.
That said, in the hands of a smith that truly cares about what his name goes on (which we hope ALL of them do), you can spend about $750 on a Stiller Predator or Viper action and you will see ZERO difference in accuracy of a custom rifle
compared to one with a McMillan, Borden, BAT, Surgeon, Phoenix machine, etc.
A trued action is just that. A "squared" action can't get anymore "square." The complete rifle and your handloading ability with good components make up the other 70% of the puzzle.
I have rifles with custom actions but most are blueprinted 700s. To date, the trued 700s are the most accurate rifles I have. That said, and to be fair, I've worked with them a little longer on load development.