Rats a cheaper. How did an Army K9 officer tell me? Rats are much cheaper, but nobody wants to be a rat leader...
But the way: The landmines very likely contain TNT. But this is not what the rat detects. Landmines don't smell like TNT...
The logistics of the rats are cheaper. But the cost basis is probably always going to be the trainers. A trainer's time is much more costly than a dog's needs.