There have been several posts over the last few years discussing this very subject (remotes for Grand L Kubotas). The Search function will help you find them.
However, assuming you want to go the Kubota factory route, here is what you need to order from your dealer to put one rear remote on an
L4330 tractor. These prices may have gone up a few dollars however.
L8305 base kit $400
L8303 valve $200
If you want to add a second and/or third remote you buy these.
L8306 second position stacking kit $200
L8303 valve $200
L8307 third position stacking kit $200
L8303 valve $200
These are dealer installed options. Installation is not included in the prices.
You can install these yourself. The easiest way is to take off the right rear tire to gain better access. It's not hard and will take a couple of hours.
There are many posts here that describe the "roll your own" remote option whereby you purchase a stand alone valve with 1 to 3 spools (like a Prince SV) and plumb it in yourself. This will be a little cheaper but not as well integrated as you will have hoses going from here to there and you have to find a way to mount the valve on the ROPS or fender.