I think the only way to determine the going price would be to put them up for auction on eBay.
I am pretty sure that the sound would not be considered audiophile quality, but the music on them might be priceless. I would pay the guy a reasonable (by your standards) price for bands that you are interested in. You may not get another chance to purchase the music on these discs.
You can also check a website called Wolfgang's Vault where you can purchase lossy downloads of concerts or stream them on your computer for free. This is a legitimate operation not a bootleg site.
I am pretty sure that the sound would not be considered audiophile quality, but the music on them might be priceless. I would pay the guy a reasonable (by your standards) price for bands that you are interested in. You may not get another chance to purchase the music on these discs.
You can also check a website called Wolfgang's Vault where you can purchase lossy downloads of concerts or stream them on your computer for free. This is a legitimate operation not a bootleg site.