If you are heavily using SQL Server features that are discontinued in SQL 2012 and if it involves huge effort to replace those functionalities then that would be a business reason.

Check this link for the discontinued features ..

http://technet.microsoft.com/en-us/library/ms144262.aspx

Also legacy DTS packages can't be hosted in SQL 2012. Suppose you have large no of packages you need to convert them to SSIS before you can upgrade to 2012.

For cost comparison check these ..

http://itknowledgeexchange.techtarget.com/sql-server/sql-2008-r2-is-pricy-but-so-is-that-other-database/

http://www.brentozar.com/archive/2009/11/sql-server-2008-r2-pricing-and-feature-changes/

http://blog.fpweb.net/choosing-between-sql-server-2012-sql-server-2008/#.UxoRK-OwKk8

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SQLBuddy