IT support benchmarks (cost)

It’s budgetting time again and I’d like to uncover some benchmarks relatng to typical support costs for the support of a user base of 650+ including mobile users, the usual PC, email, laptop stuff as well as a large Oracle installation (support and enhancements).

Of particular interest would be UK relevant sources, particularly from government, standards bodies etc and also relating to support provided via an internal department (also some of the pros of an internal department would be useful).

Apologies if I’ve just not searched long and hard enough here, but any assistance (vendor neutral) would be greatly received.