Edit to add - I'm going to withdraw the below question for myself but leave it for perhaps GP. After doing some basic tests on my largest slewing drive, I found it takes about 672 oz. in. to rotate the input shaft. So there are several moderately priced steppers available to rotate that slewing drive. Although to play it safe and not stress the motor, I'll step up to the 5 amp motors/1205 oz. (Nema 34).
This original question is no longer applicable for myself-
Is your program compatible with standard motors (with basic switching controllers) and the use of rotary encoders? If so, will an absolute rotary encoder be compatible or should it be an incremental rotary encoder?
The reason I ask is because I'm trying to save a few dollars here and avoid spending over $1500 on a single stepper motor alone as my system is using 2 slewing drives and one of them has a 3/4" keyed shaft input, the other is a 12mm keyed shaft input. Standard geared motors aren't so bad price wise (geared 3 rpm 24dc motor 3/4" output shaft - $150) in that torque range if I can incorporate a couple encoders in the frames axis points and avoid the pricey servo/stepping motors and their controllers.
If it were a smaller system, the stepper/servos and controller would be in a reasonable range.
My slewing drives are composed of a 61:1 horizontal mount (vertical axis/east-west) and a 62:1 vertical mount with Bilateral exit flanges (horizontal axis/elevation).
Here's the Vertical axis slewing drive : http://www.ebay.com/itm/NEW-TGB-TGE-Slewing-Drive-Slew-Ring-Bearing-Gear-Turn-Table-PV-Solar-Tracking-/190911995274
This is the Horizontal Axis slewing drive : http://www.acosolar.com/solar-tracker/h-fang/h-fang-precise-slewing-drive-pve3