From Schneier on Security:
Total cost for the Yemeni printer cartridge bomb plot: $4200.
“Two Nokia mobiles, $150 each, two HP printers, $300 each, plus shipping, transportation and other miscellaneous expenses add up to a total bill of $4,200. That is all what Operation Hemorrhage cost us,” the magazine said.
Even if you add in costs for training, recruiting, logistics, and everything else, that’s still remarkably cheap. And think of how many times that we spent in security in the aftermath.