Generally speaking, a three-phase generator is usually cheaper than a similar single-phase model. This is due to the alternator, since single-phase generators tend to have more power than a similar three-phase model, in order to offer the same degree of efficiency. This, of course, makes the final price of the single-phase more expensive.
This process was very complicated some years ago, but thanks to new technologies, it has become simple, effective and reliable in equal parts. Ask us for information without obligation!