Related, Hatsune Miku[1] was built with the voice from Fujita Saki[2], who was apparently offered a choice between either royalties or 50000 yen, and she chose 50000 yen immediately[3].
That might have been a poor choice financially for Fujita Saki given that the current estimated number of Hatsune Miku songs is in the hundreds of thousands, but Hatsune Miku not being encumbered by royalties probably contributed to her popularity.