You should have the hitch and rails at same time so rails can be installed where hitch sets properly when attached to rails (king ping should be center line of rear axle or slightly forward).
Installing the hitch onto the rails is just a natter of setting it down into rails slots and pinning it.
Installing the rails is more difficult.....bolted to frame and/or to brackets that are welded to frame etc. And having the rails in the right place so hitch sits in the right spot.
Who is giving you quotes of $1500...rv dealership?
Check with a local trailer shop..even weld shop for installation
Purchase the B&W hitch with the rail kit and have it installed.
My 5vr GVWR is 14,375#.....actual weight when FTng 13,830# towed with a 3500 SRW and a 16K hitch. Great combo/set up