So at last the final list of R2 additions plus price point:
BizTalk Server 2006 R2 Evaluation Edition - Free
BizTalk Server 2006 R2 Branch Edition - $1,899 (but must connect to a Ent. Edition
BizTalk Server 2006 R2 Developer Edition - $500
BizTalk Server 2006 R2 Standard Edition - $8,500
BizTalk Server 2006 R2 Enterprise Edition - $35,000
Release date: Summer 2007 (Most likely Sept 2007)
Source: WPC