A professional business mentor should be someone who has been exactly where you want to be, not to mention where you were. They need to be paid a decent wage, since they're going to be the ones helping you get to the next level. Here's what you should be aware of...

IT'S A SPECTRUM OF PRICING
It is possible to find a free mentor. I ought to know, it's happened to me. However, you usually get what you pay for. A free mentor is volunteering their two cents and will only work in their free time. If you want to get someone who will be there day in, day out, you need a professional. 

With that said, the typical range is between $50 to $300 per hour. Some, like Mark Cuban, can charge as much as $10,000 per shot!

HOW THEY CHARGE 

Most professionals will charge between $80 to $100 per hour-long session. Some offer bulk packages for around $500 a pop. For most people five to 10 sessions is more than enough to fix everything that you could get fixed.

HOW CAN YOU TELL IF IT'S WORTH IT?
You should pay a professional business mentor a reasonable price, and that all comes from their reviews as well as their results. If it's clear that they walk the walk, you can expect to see results in your own company.