I don't know if it's just a demand thing or perhaps because I don't really know what "spiral ham" is, but in Australia the only ham you're likely to find cheaper per-kilo than spam is going to be a 2+ kg leg of ham, complete with bone, fat, skin, etc. A boneless ham will be at least as expensive, and sliced/shaved ham from the deli section at a supermarket will be easily more expensive per-kilo than spam.

Of course one could argue there's an even higher percentage of inedible parts in the canned monstrosity because it's all inedible, and I wouldn't argue that view point is wrong.