That looks like a pretty sweet set-up. I want something towable behind my truck too. I've been looking for a used 5000# single axle dump trailer forever. Seems like if they're used, they're used up, and still 2-3k$. New is around 4-5k.
Don’t want to derail, but check rental yards, bought a 5’x8’ single axle a few years ago for $1350, used. New fenders and brakes and it was gtg. Sold it a few years later for $1850.