I don't know about D100,
but with D70 what I usually do is just to set mirror lock up, blow using hairdryer(cool air) and then finish off with the rocket blower. all when the camera mount is facing down of course.
Works very well, the last time I cleaned it not even 1 spot left ..
save the money rather than let the NSC do it. $23 is quite alot to me anyway.