I found (and bought) 2 new 400w SGDA drives for $80 a piece. The others I saw were all a lot more expensive (and used).
I'll keep an eye out for a deal on a third drive but I'm going to use 3.5a Nema 34 steppers with my Gecko G540 in the meantime so I don't delay my build any further while I figure out the servo thing. The Nema 34's have a longer shaft so it can reach the coupling once I mod the actuator housing.
I am assuming that there is no info out there on my servos because they were a custom order from NSK for their actuators. I feel like I have a lot of reading to do before I can use them.