When they were first published, MJ signed a batch which Julians were selling for $500 each. The unsigned versions, well much less, around $150 if memory serves. The signed ones sold out very fast and hit eBay in a matter of minutes with massively inflated price tags. I opted to buy the full set of 5 unsigned versions direct from Julians, which I still have sealed in their original shipping box. Since 2009, even the unsigned copied are selling on eBay for $500+ so who knows what the signed copies are worth!?!
Just FYI, they were all available as free PDF downloads so that's a much cheaper option if you're not too fussed about owning a physical copy??