No idea on install cost...probably around $200/250...
Are these the SRT RoadMagnets or WK RoadMagnets?
If they are the SRT RoadMagnets you should get the SRT front Bilsteins also and you will have to cut the front bumpstops in half. The rears should have come with a new set of bumpstops (mine are the 2nd version and they did).
I am going to end up getting the Monroe Sensa-trac load adjusting shocks for the rear.
This is what it will look once dropped.
I had over 320 pounds of salt in the back yesterday and it didn't bottom out and was a very nice ride. It should drop it around 2.5/3 inches all around.