It's generally less expensive on disk set strikers because the firing pin is a separate piece from the hammer.

Funny this comes up now because the left firing pin on my wife's Grulla SLE broke Saturday and I'm taking it to our gunsmith tomorrow - he'll try to locate a pin but will most likely have to make one. I have no idea on cost but that's not relevant since it's my wife's favorite gun and my first flight instructor's saying of "if mama ain't happy ain't nobody happy" applies. Whatever it costs we'll make mamma happy.