If shopping for another motor, be sure to check out Inverter Duty motors. They are very different than general purpose motors which fail miserably with a VFD as Hood describes.
They cost a bit more but perform much better with a VFD.
I use Marathon Black Max and Micro Max Inverter Duty motors.
They have 1000:1 Constant Torque operation from 0 to base speed (TENV), and 20:1 Constant Torque operation from 1/20 speed to base speed (TEFC).
I got lucky and picked up several new ones for $29 ea., suggested retail was $850 ea.
Also bought a couple new from Automation Direct.
Real workhorses.
Good luck,
Russ