Hondo,
I have no clue what your JD dealer will charge you.
There are tons of threads about doing doing it yourself though. While you're at it, get at least a 2 or 3 spool valve instead of just a one spool. That way you'll have extra remotes for other hydraulic implements or for hydraulic side links or something. The cost of the valve is not that much more nor are the extra hoses once you start plumbing it into the system.
Cost to do it yourself would be about (approximately)
$150 for the valve (cheaper for a 2 spool and cheaper for a single spool yet)
$100 for the hoses and fittings to connect into your system
$100 for quick disconnects and hoses coming from the new valve.
Add the cost of the top link to that depending on whether you buy one from CCM
CCM Top Links or make one yourself.
I would also plumb a pressure guage in there for about $16 too.
If you're handy, you can make your own bulkhead bracket for the QD's
So all it takes is your time to do it on weekends.
Compare that to what the dealer wants to install.