Just to be clear, installing a diverter valve or electric over hydraulic is almost always more money than installing a rear remote.
No doubt the cheapest solution is if you already have a rear remote and just running 1/4 inch or 3/8 inch line from the remote forward over the rear axle, under the operator station, up the left FEL mounting post and down the FEL arm to the torque bar where you make a QC connection to the
grapple. Takes about 20-30 minutes and a bunch of zipties to set that up.
Installing a rear remote if you don't have one can be fairly straightforward and many guys have done it in a couple of hours even without prior hydraulic experience. It does depend a lot on what the tractor manufacturer charges for the kit. I only am familiar with Kioti who make a kit for about $350. Several posts with photos on installing that in the Kioti section. Other manufacturers charge more and I recall NH has an outrageous fee. One point about the rear remote: make sure the control lever is conveniently located on your tractor: it should be possible to drop your hand off the FEL controller and reach the rear remote without looking....think 4 on the floor shifter or something natural like that. You don't want to have to look or put your hand in an awkward position to rear the controller.
Diverter valve kits are available from WRLong for something around $500 which come with instructions. WRLong only sells through dealers but any dealer can get you either the kit or can install it for you for 2-3 hours of labor. That is probably the middle ground in terms of expense unless you are brave and want to just source all the components yourself in which case you can probably save $100-150 by getting similar stuff from Surplus Supply and save more by doing your own labor.
Electric over hydraulic is the Cadillac of solutions. Figure about $1000 for a WRLong kit plus dealer installation.
If you don't have a rear remote consider this as an opportunity to kill two birds with one stone. A rear remote is very useful for operating a hydraulic topping lift and can also power other devices such as a log splitter. If you do driveway maintenance consider putting in two so you can do top and tilt.
Regarding which is best, no one seems unhappy with any of the three methods for controlling a
grapple. I have personal experience with rear remotes and diverter valve. I think they are about the same. Electric over hydraulic would be nice but I'd rather use the extra cash to have an extra implement than the slight additional benefit that valve provides.
