Just doing a quick web search, it looks like the tiles would be anywhere from $12-$24 per coping piece. If they're 24" long, then you'd need at least 60 (depending on cuts/curves). So, you're looking at about $1k+ just for the coping. If he can replace your coping, expansion joint, and fix your tiles, for ~$5K, that sounds reasonable. I mean, it's not astronomical, but you may be able to haggle with him a bit. You could have him replace just the hollow coping, but then you have to worry about matching the old with the new. If a lot of coping needs to be replaced, then I'd replace it all.