Numa Compact 2X is an okay starting point on a tight budget, but we can do better here. Limitations from a prog rock organ/synth and learning perspective are that the organ/Leslie sound is so-so (particularly weak on overdrive), synth editing is limited and menu-based, and there's no monophonic lead function (including no portamento).
Since we're also talking about used options, another board in the "entry level" category and price range would be the Casio XW-P1. It's only 61 keys and has no aftertouch, but its synth functions (both monophonic and polyphonic) are much stronger; synth editing functions are still menu-based but it has the advantage of having a computer editor; organ still has Leslie/overdrive issues, but you can address that if/when needed via an external pedal. Adding the pedal is more viable on the Casio than the Numa, because the Casio lets you pan your sounds to one side of the other, meaning you could put the pedal on just your organ sounds (which you'd have panned to one side) and not worry about other sounds going through it (since they'd be panned to the other side), a flexibility that the Numa doesn't have. Both boards are respectable MIDI controllers, letting you use their 9 sliders for MIDI functions. (In fact, the Casio supports 4 MIDI zones, while the Numa supports 2.) I also like that Casio lets you select sounds with buttons, whereas the Numa depends on the scroll wheel. That Casio was one of my favorite budget boards, it's a shame it's been discontinued. (As for the Numa, it retains advantages in its sampled sounds, so, for example, it's much better for pianos/EPs.)
Still for the task at hand and available budget, we've covered better stuff here.
