From Inside Microsoft Dynamics GP comes New Pricing for Microsoft Dynamics GP 2013 Announced
New Pricing for Microsoft Dynamics GP 2013 Announced Today – Inside Microsoft Dynamics GP – Site Home – MSDN Blogs
Microsoft & the GP EcosystemGP 2013
Archived post from 2012. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.