In case of the Chinese, when I was at sea, I heard stories of massive prisoner ships that are essentially used for slave-labour at-sea. That time it was for fishing (massive mother ship with smaller, still huge ships spreading out to empty out the seas in waters very far away from China).

If they would engage in sand stealing, the prisoner slaves might help keep the labour cost down.

A big slow barge can carry $200-500k, depening on how big the barge is. That's a fair amount of cash.

From there, you've got 40-100 truck runs from wherever the barge unloads to wherever the sand's in use, assuming you can't run the barge straight to the customer. Again, that's not a huge amount +to the CFR above.

Above using barge capacity of 20-50k tons, and truck capacity 50 ton.