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It's not a synthesiser unless its actually synthetic technically. Vocaloid is a sample and pitching framework that uses real vocal sounds. Vocaloid will be quite expensive due to this, it's also hard to resell because Vocaloid demands the sounds you apply don't sound equal to the pack and they don't want people getting those sounds cheaper than the library price. There are other frameworks without the issue but are not quite as verbose.
No one asked you to read Billy, that was unnecessary, I'm just trying to be helpful I don't need to you know some people pay for that kind of information.