While Nintendo's said it would help ensure that DLC pricing isn't unreasonable, Square Enix shows us the future. One downloadable song for Theatrhythm Final Fantasy is ¥150 (US$1.95); all 8 tracks are ¥1,200 ($15.60) Not cheap! [忍之閻魔帳]
This is partly down to the strong yen, though. In Japan that would still seem relatively reasonable. Five years ago ¥150 was $1.24, so all eight tracks would have been around $10. I would hope that when these tracks are released in the US and Euro versions of the game the cost will drop slightly.