Hey Shane,
in any case if your budget is limited, I would spend more money on the VFD than on the spindle. The spindle will be gone one day, as it will accumulate dust in the bearings (except if you have one with sealing air), it is subject to wear, but the VFD is there to stay. And the more smart and sophisticated the algorithms inside the VFDs are, the more performance will you get out of the spindle.
The Omron MX2 (that I bought) is identical to the Hitachi WJ200 except that the Omron can deliver 580 Hz for speeds higher than 24,000 rpm. I bought the matching filter and the brake resistor with it as a bundle here.