I hate to disagree, but I've bought quite a few Mosaic's on eBay, and I've never paid anywhere even close to $50 a disc, record or CD. Some do go that high, hence the "eBay Madness" thread, but it's just that, the madness of auctions, and not the actual value.
Sometimes I've gotten steals and other times I've had buyers remorse (Commodore's, I'm looking in your direction...) but I've found every set comes up more often than you'd think, and as long as you're willing to let it go, eventually you'll get it for a fair price.
I would say around $60 to $75 would be fair for the Herbie Nichols set.