Making three phase is possible and fairly easy. Don't let the disconnects, contactors, and so forth phase you because you don't need to be this elaborate. We simply had access to the parts for free. Small 3 phase setups often don't even need a single phase startup motor you can simple get them spinning by giving them a kick or with a start capacitor.
Here is a video of our setup: [nomedia="http://www.youtube.com/watch?v=WNP1smG2xjI"]YouTube - ‪Picture 054‬‏[/nomedia]
30HP 3 phase motor
1HP 1 phase motor
A few pulleys, a belt, and some wires etc.
How it Works:
The 1HP single phase motor spins up the 30 horse power three phase motor (otherwise the inrush current will trip your breakers) then a series of contactors open and close to disengage the small motor and apply power to the large motor. Once power is applied to the large motor it generates the third phase on the third leg. We balanced the phases by trial and error with capacitors until all legs were within +-2 volts.
This video was taken before we wired in a 100 amp feeder directly from the house panel. We can run our Hypertherm 1650 at a constant 85 amps.
Feel free to PM me if you have any questions.