No matter which RPC you get, keep money in the budget for capacitors to balance the output of the line inputs and the wildleg output of the phase converter for your mill's horspower load. Make sure that the computer side does not connect to the wildleg or generated phase. The computer should be on one of the legs from the line.
You may want to make sure that the manufacturer has no warranty problems with you balancing the output to your load, if they did not balance it for you.
In the Phase Converter Forum there is a thread from five weeks, ago,with some used "CNC rated" rotary phase converters for sale that might be able to save you a couple of dollars, if, he still has them for sale.
http://www.cnczone.com/forums/showthread.php?t=37547 (I have a couple used phase converters)