As project-managers try to be smart (and cheap) when it comes to buying software used in fixed price projects, I feel the need post the following:
BizTalk Server is sold in 4 different editions as you can read on microsoft.com/biztalk. But note that you cannot use a Partner Edition (approx. 1K Euro) without a Enterprise Edition. This Partner Edition is only for partners of a company which has an Enterprise Edition.
I know, it's not mentioned anywhere on the BizTalk pages, but I heard it from a Microsoft employee myself. So the cheapest you can get is a Standard Edition (approx. 6K Euro). See the 5K profit gap in the project calculation.
from microsoft.com/biztalk:
Enterprise, Standard, and Partner Editions
BizTalk Server 2004 Enterprise Edition is designed for customers who require high volume and high availability, and scalability to an unlimited number of CPUs. This edition supports integration with an unlimited number of internal applications and external trading partners. BizTalk Server 2004 Standard and Partner Editions are intended for small-to-medium deployments, and are limited to a single CPU. BizTalk Server 2004 Standard Edition supports integration with up to 10 applications and 20 trading partners. BizTalk Server 2004 Partner Edition supports integration with up to three applications and three trading partners.
Developer Edition
BizTalk Server 2004 Developer Edition is limited solely to designing, developing, and testing purposes. You may not use it as a passive failover server or for disaster recovery.