Open Source (free) or two commercial editions, pricing for Enterprise Edition is: Annual: $695 / socket, Perpetual: $1525 / socket - both including 1 year of software maintenance
For commercial editions (Standard or Enterprise)XenServer is licensed on a per-CPU socket basis. For a pool to be considered licensed, all XenServer hosts in the pool must be licensed. XenServer only counts populated CPU sockets.
Customers who have purchased XenApp or XenDesktop continue to have an entitlement to XenServer.
In XenServer 7, customers should allocate product licenses using a Citrix License Server, as with other Citrix components. From version 6.2.0 onwards, XenServer (other than via the XenDesktop licenses) is licensed on a per-socket basis. Allocation of licenses is managed centrally and enforced by a standalone Citrix License Server, physical or virtual, in the environment. After applying a per-socket license, XenServer will display as Citrix XenServer Per-Socket Edition.