Didn't know they'd got that cheap yet (still get ripped for a fiver deposit on a transport one here, *******s), but that'd suggest the postage would be dearer the cards in the volume we'd need.
They clearly can't be too dear to make, as the FAI replace my also FortressGB made card annually despite having had the same seat for a while now. And their financial situation is incredibly poor, so you'd think they'd go for obvious savings.