One caution: SPAM isn't actually cheaper than ham, it's just shelf stable without refrigeration. You can get a decent spiral ham for well under $3.29/lb (Costco earlier today), but 12oz cans of SPAM work out to around $5/lb.
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.
A spiral ham is actually a spiral sliced ham. This is the butt end or shank end of a whole ham and yes, typically probably 3kg at a minimum. The 'spiral' part is that during processing it's been sliced in a spiral that leaves slices roughly 5-7mm thick. These are typically a little more expensive than unsliced bone in hams, but the convenience factor is huge.
Hams like that often go on sale around US Thanksgiving and Christmas, with prices for them around US$4.50-6.50/kg last week and probably as 'loss leaders' around US$2-3/kg the week before Christmas. Ham is a regular part of 'traditional Thanksgiving' but not as much as turkey, whereas the 'Christmas ham' is definitely a thing.
