I've repaired a few broken necks in my time, and the type of glue you'd use depends on where the break is. For almost all repairs, a bog standard wood glue will work fine - the glue will be stonger than the wood ever was. If it's broken around the nut, I'd use epoxy resin to make sure, just because you haven't got as much wood (and therefore surface area) to apply the glue to.

I've repaired numerous Ibanez Wizard type necks with ordinary wood glue from homebase and never had a problem, although you'd still need to declare the repair on ebay or face the possibility of an unhappy customer...