"Trafigura, Vitol and BP exporting dirty diesel to Africa, says Swiss NGO
"Traders blend cheap fuel with sulphur levels many times the European limit for sale in African countries, says Public Eye"
[0] https://www.theguardian.com/world/2016/sep/15/trafigura-vito...
Where I am, a ton of sand aggregate using in construction is ~$100 per ton. The better sand used in gardens, the brown sand (it's used to repel water so you don't over-water crops) is more than than.
Considering the wheat/ton spot price is $160 per ton at the moment, I don't think the actual prices would be too different.
[0] http://www.indexmundi.com/commodities/?commodity=wheat&month...
Also, diplomatically, this might be more difficult to defend. Although allowing this would've been in the best interest of both nations. Cue the human condition :)
I'd say that feeding humans or even livestock is more important than profits. Or at least, it ought to be.