New they are worth a few bucks, there is a used hardinge spindle amp on eBay right now for over $1,500.00, and a new one will cost upwards of $3,000.00, if you want to go new, contact your local Baldor dealer and give him the specs.
Perhaps a more cost effective way is to go VFD and a three phase motor, There are VFD's now that will come close to DC motor control with high torque at zero speed etc. if you go with a quality product like Mitsubishi or WEG.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.