I would like to see the content be available in some other way unless they do turn out to be common and Nintendo makes the squid available in all regions seperate from the 3 pack. I'm not too interested in the missions myself as I'm expecting to focus more on multi player than single player, although that could end up changing, but I am interested in the unlocks so I can use them online. I've been trying for a fairly long time to get the 3 pack but keep missing it when available so I'm currently preordering the Inkling Girl so at worst I'll at least have her things. It would be nice to have some way of getting the rest of the content and without having to repay for the Inkling Girl if I can't find a 3 pack prior to release but find one after.
For price, it's hard to say without knowing the length of time the content will last and what the unlocks are like, but I think around $7-8 would likely be fair per amiibo's content. An alternative would be to sell content more specifically, like say $0.25 per mission and maybe $1-2 per mini game.