Depends how rare and popular the guitar is. Figure out how much it goes for new vs used. you can expect the same price difference between Used vs neck break repaired.
personal example from experience:
Epiphone Wilshire:
New: $550 Used: $300
Used w/neck break repair at the heel: $155
No don't want to sell it, it's the best looking and playing LP I've ever had. Just trying to figure out if I payed a fair price. The guitar was repaired by glue injection then clamping. The headstock was cracked not broken completely off.
Yep.That's pretty much the price i thought i would sell for. if the repair is unnoticeable you made out great!