Okay, after actually reading the manufacturers specs on this motor, I'm going to change my tune - a little. You do get the servo drive built into the motor, along with the speed adjustment and forward/reverse controls. You can't see them in the picture shown in the link, but if you go to the manufacturers website you can see them. The servo drive is that big honkin' thing on the back end of the motor. At this price for a 3/4 Hp variable speed motor it might be worth looking into if you wanted to experiment.
I would have three concerns about this motor. First - I haven't been able to find whether it's rated for continuous duty or not, this may or may not be an issue to you, depending on how long and hard you intend to push your mill/lathe. Second - I couldn't find anything that would give me any idea how good of speed control you would get. That is to say I don't know what is going to happen under load. For instance, you might have the motor speed set for 2000 RPM no load and when you put a load on the motor it might drop to 1000 RPM. Third the motor mounting bracket looks very unique to put it mildly, you'd probably want to do something different.
Don