Most if not all GM rotors, after you cut down the to fit the removable rotor, the 3.06"ish" machined stub in the middle is not long enough to line up the Impala wheel.
They are barely long enough stock and the added thickness of a hat on top is usually enough to prevent it getting to the 3.06 part of the rim.
As for who does the machining, if you can't do it yourself and have to pay, then buying already machined, redrilled rotors would make more sense.
Kore is what I would do.
http://www.kore3.com/products.php?cat=24
Also, when you compare apples to apples the kore full kits are pretty much "right there" on pricing.
Just over a grand but the ABS works, the hubs are billet, the car doesn't get wider, correct bolt pattern