Well this one is like $60 shipped
PRX - IGBT CM600HA-24H Power Module 1200V 600A - eBay (item 290049066472 end time Apr-27-09 14:17:07 PDT)
I guess the "dual" response would be, how much efficiency gain are we talking about, and is it only at full throttle, vs cost/complications, ya know. Is it good enough to get started with, kinda sounds like it will handle 48 volts 300+ amps no problem. Throw some pwm at it and monitor the current I recon.
Also the synch gains are probably frequency dependent.