Lance does many things that Avery can't even fathom doing on a good day. For one, Lance can create for the others around him. Avery, despite the incessant attempts, has not emerged in that aspect. Lance is a very multi-dimensional player, whereas Avery is a one-trick pony.
Also, echoing what many previous posters have pointed out, AB is a niche player; he needs the "correct" system around him to excel. I think that Lance is the type of player that can do well in any situation, given that there is leadership around him. His history suggests that he can be a source of trouble if he's not under the right supervision.
I really don't think Lance should be the anchor to compare Avery's potential contract amount. I'd say that a more equivalent player to compare with would be Iman Shumpert (despite his struggles this season) and Jimmy Butler.
But to answer your question, given Avery's potential and age but also taking into account his one-dimensional skillset, I'd say around 5-6 million per would be fair value for him going forward. Looking forward to see how he plays when Rondo returns.