If you want to run a VFD, I've used a TECO FM50. It's a nice little unit. They make them with 120v input, 3 phase output up to 1HP which is what you have.
http://www.factorymation.com/Products/FM50_115V/FM50-101-C.html
I ran mine like that on my powermatic 1200 for years. Then I upgraded it to a start/stop, reversing, jog and speed pot. The reason is simple. With just the regular push button VFD, changing speeds you need to press those tiny little buttons.
So you wire up a 10k pot (don't worry I had no idea what it was either but radio shack and eBay do...

). I bought some push button switches and the fwd/rev switch and the jog button.
So now I can turn a dial and the speed goes up and down. I can flip a switch and reverse the press. Or I can preset the jog button to jog the spindle fwd at 10rpm for tapping. It's fairly easy to do once you have the manual in front of you and it makes using the drill press so much nicer. I should put the VFD in an enclosure now that I don't need to press and buttons one of these days
Here's a video I did a couple years ago when someone asked me about wiring up a VFD and adding the added functions I described above
Edit: one last thing...be very careful to ground EVERYTHING including the actual VFD case. I was getting some stray current enough to make you say hmmmmmm and get a tickle before I got mine grounded correctly.