Would building a training saber be a lower difficulty than a regular/full powered one?
Niil's got the damaged one so he and Collan should have a good idea of the parts required, which are listed in this older thread, which also states Niil knows what crystal(s) he could use.
Niil and Collan might be able to convince Trax to let them have a look at the one he's got. Using it as a guide might provide a bonus of some sort. Just remember, with Trax, bribery works better than flattery, and extortion will get you killed. 
Heh . . . oh, that should be fun. Niil working on a fully functional dark Jedi blade with a Mechanical level of 2D (2D+1 if I can get a pip in Lightsaber repair).
Niil: "Hey Collan, I think I've got this figured out! See, this is where the focusing chamber is! Look at how the crystal is aligned, though . . ."
<. . . Niil accidentally nudges the crystal out of alignment . . .>
Collan: "NOOOOOOOOOOOOOOOOOOOOOOOOOOO!!!"
VOOOOORSHHHHHHHHHHHHHHH!Three hundred meters away in the cavern complex, Trax looks up from his meal in the cantina as the floor shakes and a hot wind blows down the corridor. Snorting and shaking his head, he returns to his meal . . .