I switched to my US account and now the pricing appears right.
Each song costs 0.99, each song bundle from each numbered FF costs 2.99 and each character costs 1.99 USD.
There's currently 25 buyable characters, so buying all of them costs about 50 USD.
There's currently 13 music bundles that give you more or less the same music the vanilla 3DS version comes with, so buying all bundles costs about 40 USD.
Finally, there's currently 59 single song purchases that are more or less the same offered in the 3DS versions as paid DLC, so buying all of them costs about 59 USD.
That means... that buying everything availiable right now would cost you about 150 USD.