The mentor issue keeps coming up on BP so I thought I would provide my take on it. The original use of the term mentor comes from Homer's Odyssey. When Odysseus, King of Ithaca went to fight in the Trojan War, he relied on his mentor to look after his kingdom. Mentor served as the teacher and overseer of Odysseuss’ son, Telemachus.
The Merriam-Webster Webster Dictionary defines a mentor as "a trusted counselor or guide."
When I think of applying or receiving mentorship I think a key concept is that it is not for the personal gain of the mentor. It is this concept that makes the mentor/protégé relationship a special one. Based on this idea I do not believe someone can pay for a mentor, as that relationship no longer exists. You may be paying for similar advice or guidance but the special relationship is not there given the "mentor" is involved for his/her own gain.
This is not to say a mentor cannot gain from the relationship, as it should be a mutualistic relationship, where both parties benefit. That said, it is the intent of the "mentor" that is key.
This of course is just my take on the mentor issue, based upon my own experience as both a mentor and a protégé in real estate and other situations in life.