To buy a new one complete like a Mcmillan, Robar, Brown Precision, or to buy a Rem 700 and build one up? The Above companies run about $3500 each, that's about all I'm willing to spend on a tactical rifle.
If you get one built up from the same maker, you might save a little if you could find the action for a low price. Or if you get a complete gun, say a 700 BDL or a PSS you could sell the parts you're not going to need and save yourself a few bucks that way. Regardless, we're probably only talking about a couple hundred bucks at best.
And I agree also that GA Precision is a great riflesmith. Their rifles are among the best I've tried. This includes some Robars, AI's and Chandlers.
Back to the point of the thread, however, my experience is that there is not a significant cost difference between buying a "package" gun from one of the top manufacturers, or starting with a bare bones Rem 700 and having it built out.....assuming similar features and quality.
The advantage of having it built up yourself is that you could spec out exactly what you wanted and didn't want as far as features....assuming you have enough knowledge and experience to be able to do this.
The advantage of the package gun is that they are typically made with all the features you need and none that you don't. These guns are built by highly experienced people and you can be assured that they will put together a well integrated gun with super performance.