They are standard clay balls with a moderate amount of cracking and missing the four ball. The cue balls are a good addition. Complete sets in good condition were selling for about $90-$150 when I was following them on Ebay. I probably have a spare 4 ball if your buyer wants to complete the set, or you can probably find one on Ebay.I have no idea what they are worth so I cant put a price on them yet. Make me an offer and you never know.
Sometimes it's a matter of finding just the right interested party.
They may not be worth much to anyone else.
But your old balls may still have plenty of life in them.
As long as you have taken care of them.
As long as you keep them polished.
As long as they are still in their original case.
Just hang on to them, it shouldn't hurt.