...but you still need Amiibos.
http://www.nintendoworldreport.com/news/40433/animal-crossing-amiibo-festival-to-be-free-to-play
It appears that the only cost of entry to the Animal Crossing Amiibo Festival is itself the Amiibo.
According to Youtube personality TheBitBlock, the game will be a free download that just requires the Amiibo to start.
BTW I found out that Animal Crossing Amiibo Festival is a free download game. Amiibo are required to play though. #E3
— Josh Thomas (@TheBitBlock) June 17, 2015
Retail bundles for the game are listing on websites, but the bundle has already been confirmed to include two Amiibo and three Amiibo cards.
Does that explain why gameplay seems to be... missing? Video I saw showed basically no meaningful interaction.
I guess this is "free-to-play" in the same way that Amiibo-Tap is free-to-play. However, unlike Amiibo Tap's always-on-a-timer experience, this actually seems like a full end-to-end game. And let's not forget that Amiibo Cards will work just as well as Amiibo Figures for the game!
Awesome! I missed that bit.
It's not just pure luck, I think there is some element of buying and selling turnips or something.