Most professional Vocaloid software offers time-limited trials to let you test the interface and voicebanks before purchasing. VOCALOID6 Trial
Strictly speaking, is a proprietary engine owned by Yamaha, and official voicebanks (like Miku, Len, or Luka) almost always require a paid license. vocaloid voicebank free
Many producers find that "free Vocaloid" isn't about the official Yamaha brand, but rather powerful alternatives that offer similar—or sometimes superior—flexibility for $0. and official voicebanks (like Miku