I think a wand is cool enough just for getting to cast a spell 50 times. That's what the DMG cost is for. If you made it rechargable, I would make it more expensive.
I'd probably allow it so long as they paid the xp as well as the gp costs. Otherwise you are making wands more powerful. And you'd better be prepared to answer the same question with repsect to staves, rings, and anything else with spell charges in it.
Edit: Oh, and they'd need the "Craft Wands" feat in order to do it.