The extractor is only a $20 (retail) factory part, plus another dollar for whichever extractor spring is needed to get the tension within the necessary range. Of course, you have to factor in shipping & labor, as well. It's about a 10-20 minute job, depending on how much time is needed for filing & checking fit & tension with the bar gauge and force dial gauge while fitting the extractor. (They used to have armorers use another gauge when fitting extractors, called a flag gauge, which checked Go/No-Go tolerance of the dimension between the inside of the extractor's hook and the breech face behind it, but they don't consider that gauge check to be necessary anymore.)
I heard from a fellow one time whose agency armorer apparently didn't think it was necessary to fit (or at least check for fit) 3rd gen extractors in their 5906's. Apparently, they started experiencing failures-to-extract after new extractors were simply dropped in some of their guns. (Over-filing the extractor's adjustment pad can result in the opposite problem, where the extractor is so tight that feeding problems can occur.)
The tolerances of the newer production 3rd gen guns are supposed to be tighter than the older production guns. CNC is a good thing.
I've had some older 59XX's which required quite a bit of filing on the new extractors to get them to fit and function properly, and then some of them required only a little filing in order for them to work right.
Also, in the older slides, which had the extractor spring holes cut by a hand-controlled operation, the depth and shape of the bottom of the hole could sometimes vary. There were 2 sets of "repair" extractor spring kits offered for use in the older slides if a standard new spring couldn't produce the necessary tension.
One kit was a set of "nested" springs, with a tall/thin spring nestled inside a 'normal' length/diameter extractor spring. The taller spring reached into the bottom of the hole at the center, which might be deeper than the outside edge of the hole. I was told by the factory that a hand-turned ball end mill tool of the appropriate diameter could also be used to correct the shape of the bottom of the hole in a problematic slide, but it required attention & caution in doing so (and wasn't taught in the armorer class, since using the "repair" spring kits was easier and wasn't likely to let the armorer cause damage to the slide

). This nested spring kit was eventually rendered obsolete when S&W started sending out a different 2-spring kit, where the 2 different standard dimension springs, of different strengths, could be tried to see which produced the necessary spring tension in a particular pistol.
I used quite a lot of the older nested extractor spring kits to repair early production 59XX's.
