What CalG said. With spindle and hydro motors running steadily and workhead and coolant motors running intermittently (most jobs) there are few, if any simple, practical alternatives to a rotary for full power 3Ph operation w/o hiccups. btw, VFDs and similar options are one/motor, such as on a manual machine with just one for the spindle.
The ultimate would be 'Phase Perfect', but could easily cost more than a decent used ODG. At the lo-buck end, and as good as anything, source a 3Ph motor from CL, ebay, or Surplus Center and find 'Phase Craft' for the other bits, and for noteworthy assistance on all aspects of matching converter to the load/machine.
Somewhere between the extremes of investment are 'package' RPC setups, plug and play if you will, with 'box' and motor. Shop carefully, and look for reviews on sources or models. Also, Google 'phase converter' and look for anything from Practical Machinist, where us handwheel-spinners join the CNC guys in a 3ph-specific forum.
Building an RPC is only daunting the first time.