The cheapest I've ever found ZBrush, other than that Daz sale that just expired is:
http://www.sharbor.com/products/PLON0310006.html
However, you can also get a deal from Kurv Studios right now for ZBrush 2, which, I think, still entitles you to a free upgrade to Z3, but I would double check with Kurv/Pixologic just in case.
http://www.kurvstudios.com/Merchant2...Code=pixologic
$399 if you don't need the printed manual.
ABC