I wouldn't bother truing the action if you are using a pre-chambered barrel, especially if it is also pre threaded.
A big part of accuracy is to use a match grade barrel and chamber and thread it using the latest Benchrest Gunsmithing methods getting the chamber and threads centered on the area of the barrel where the throat will be.
In truing an action it is often thread slightly larger and pre threaded barrels will have a loose thread.
Labour for truing 700 actions and and chambering and fitting barrels may cost anywhere from $300 to $600 I would guess.... it just depends on who, how much to be done and how well you want it done.
A quality barrel in most larger calibers with no truing work done to the action will often shoot 1/2 minute. Smaller more accurate calibers in the .300's.
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