I love the VFD set-up on my Jet 1642. I hated the step pulley system on my small metal lathe.
E-Bay was the answer.
After browsing the offers for various drives and visiting the manufacturer's websites for wiring schematics and other information, I purchased a used 3-phase motor for $20 and a Hitachi VFD for $99. Other than some tweaking to fit the motor and adapt the pulley, the installation was easy.
If anything, they make the manuals for the VFD more confusing than need be for neophytes (like me).
Step one is to figure the wiring which is basic and straight-forward. Step two is configuring the drive for your motor (number of poles, is usually all that is necessary as the rest of the factory settings should b OK) and whether or not you have some form of external control. Since I wanted to mimic the set-up of the Jet, I added a remote E-stop button, a FWD/REV switch and a speed control pot. This was more or less like programming a video recorder or digital clock.
I certainly can see why some retailers charge good money for a package price on a variable speed drive system: it takes some time to set it up and they probably have to account for tech calls and the like. But if you can strip wires and solder connections, you can hook up a VFD.
One word of caution: make sure you can fit whatever motor you're buying on your lathe. You can find many 1 and 2 hp motors for cheap, but they may be in the same size case as a 3 or even 5 hp motor.