How to value a used CD collection?


I have a pal that digitized all his CD's and is looking to sell them.  Approximately 500 high quality jazz CD's.   I expect he will be looking for a price for all of them.  I'd be keen to have them, but have no idea what that sort of collection is worth.  Maybe $5 a CD?, but he has lots and lots of stunning recordings that cost $30 or more.  Any insights would be appreciated.  Maybe I should just asked to match his best offer and see what happens.  

Any insight would be appreciated.  Thank you, Mark  
whitestix
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whitestix
elizabeth offers good advice. If the CDs are on an Audiophile label (DCC, MFSL and others) those discs will increase in value. Make your friend a best offer and see where it leads. I would be interested in learning more about his collection as well.
Happy Listening!
Ladies and gentlemen,
This potential purchase is a vexy one for the reasons you have mentioned.  I appreciate the feedback.  

Selling CD's on Amazon is a losing proposition with the nick they take out of the sale. I guess I need to investigate other less costly site to sell CD's if I acquire this collection.  

As an former market trader, what occurs to me is that will offer to match the best offer he gets for the lot of his collection.  I think that is the easiest way to value his collection... all at wholesale.  Cheers.  
is it an arms length transaction between market traders or a deal between friends ? I would offer what I felt was fair, add a bottle of Rye or Seasmoke and enjoy the good music and Kahrma....

Discogs provides statistical valuation ranges, however shipping on small orders can often exceed Cd value even w USPS media rates...you might figure that into the bottle of Rye