His value is pretty low. A pretty objective third party writer through together some trade proposals.
http://www.nba.com/article/2016/12/26/morning-tip-what-should-sixers-do-nerlens-noelHere are his ideas
Noel + F Timothe Luwawu-Cabarrot for F Ed Davis, G Shabazz Napier
Noel + SF Robert Covington to Toronto for SF Terrence Ross and 2017 first-round pick (LA Clippers)
Noel to Oklahoma City for C Joffrey Lauvergne, G Cameron Payne, F Josh Huestis
Noel + future second-round pick to New Orleans for PG Jrue Holiday
Note that Holiday will be a free agent also at the end of this season. There isn't a lot of value for Noel or Okafor as much as the 76ers wish it wasn't true. For whatever reason it seems like Ainge doesn't want Noel or he would already be here pretty cheap.