AC drives

Hi all,

Most of people use either steppingmotors or DC-servo, I noticed that
the big manufactures (fadal, haas, dmg etc.) all use AC-servo. The
benefits are more dynamic, more compact, higher peak torque. Are
there any step and direction AC-drives out there, or is the price too
high.
AC-servo motors are synchroonmotors while a regular AC-motor (like
the spindle motor) is asynchronic, right? Could it be possible to use
a regular AC-motor as a drive motor, these motor are very cheap and
deliver a lot of power.
Just an idea,

Hugo