you rent a dump trailer, likely total cost is less than purchase..over a number of years.
However, you purchase a dump and you will find other uses for it. If it is an over the road dump, you find yet more uses for it.
My case, I purchased a used 20 ft gooseneck dump, 10 ton payload, $7000 off Craig's List. Has self contained pump, reservoir, battery, works fine, battery will last for 4-5 full dumps before needing recharged. Discovered over $3000 worth of building stone that a builder had left and wanted moved (free to move)...so, used my FEL, forks, pallets, loaded stone on pallets, pallets into dump trailer, multiple trailer loads... was able to use dump feature to encourage pallets to slide to rear of dump so could be picked up by FEL/forks. I don't use it too frequently, but handy when I do... and don't have to go rent it:thumbsup:
If you get trailer with battery driven hydraulics, need to run a BIG wire from pickup battery back to trailer so it can be recharged while you are driving...need to do real electrical calculations on size of wire... mine is about size of my little finger... anything smaller will get hot.. lots of amps drawn when battery has been discharged....disconnect from pickup when using battery power to dump, will draw from alternator or pickup battery too much if you do not.
Consider gooseneck versus bumper pull... and your available tow vehicles...gooseneck safer for over the road, pickup pull/heavy load. Bumper pull better for moving with tractor (little down force on tractor rear, thus losing steering, vs 3ph gooseneck ). But, tractor brakes not up to dealing with a really big dump load, IMHO, need to use engine brakeing, go slow.
You have lots of sand, I'd use it. WOW... you can't even PAY to have the road worked on... makes it clear, if it's gonna happen, you are going to do it... means you gotta do it when weather conditions are favorable for doing so...means it's better for you to own a dump trailer so you can do it when time is ripe...be aware that a loaded dump trailer is really heavy... easy to get stuck if you don't have sufficient traction...4wd critical, IMHO, for your off road tow vehicle.
If using tractor hydraulics, you are committed to dumping ONLY where your tractor is. Also, this mixes (may or may not be a problem in your mind) your tractor hydraulic fluid with the dump cylinder fluid..and likely that dump hydraulic cylinder will require more fluid than typical farm hydraulic cylinder.... dunno if your tractor hydraulic tank is sufficient size to handle...
Just some thoughts