I didn't see anyone mention this possible solution, but for guys who like to keep it simple, yet do it right, it might be a good way to go: I met a guy who works at a big motor repair center. He rebuilds (don't know how) used motors into 3-phase rotary convertors, and sells them for around $100 for a 5 hp unit. He claims they have the same efficiency and performance as commercial units (?). Surely he isn't unique in doing this.