I recently saw a pretty good product for a affordable price.  SQLSpec from Elsasoft (http://www.elsasoft.org/) was actually written by a member here http://www.sqlservercentral.com/forums/userinfo.aspx?id=145142.  It does not do HTML Help files like ApexDoc, but seems to cover the features pretty well.  It can also help to document application access (though you have to put the links and info in via an additional XML file).  And for $50, it certainly more affordable than the others listed here.