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  
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 might figure that into the bottle of Rye

Sorry to throw a spanner in the works here, but if you rip your CDs, my understanding is you have to keep the cds as proof of ownership and your right to rip them in the first place. If you don't, you could be prosecuted, unlikely though that might be.

 Secondly, even if you back up the rip, you might want to re rip your collection to a higher quality storage medium , as I did.

 My concern is a more depressing one, what happens when I fall off my perch, I'm 70+ now. I have about 2500 LPs and the same number of CDs. I don't want to burden my kids with getting rid of them. Amongst that lot are some valuable albums, MFSL, Proprius, Opus, FIM and so on. Dealers I know, will rarely take whole collections and will give a derisory sum if they have too. So, any thoughts?

 The plan at the moment, is given some warning, to go through the whole collection, pulling out what I think is valuable and suggesting to the kids to E=bay them, or do it myself. For the rest, I would advise them to get dealers in and let them chose what they want, perhaps the rest can go to charity shops. takes less of a slice of the pie than either Amazon or eBay.

Reverb is cheaper still but not as well known as a site for consumers for buying used media ... Yet.

However one downside of secondspin is that just about ALL the cds on there are dirt cheap to start with.