Replacement for 10 speed Shimano rear mech

chriskempton Posts: 1,245
edited January 2010 in Workshop
I know this has been done to death but there is much contradictory advice on this so wanted to ask......

My Ultegra 10 speed rear mech died a sudden death this morning, what can I replace it with? It's my winter bike so cheap would be great, happy to get an 'inferior' replacement. Rest of group is Ultegra 10.

Can I use a Sora 8? A Tiagra 9? A 105 9? An old Ultegra 9?

Or do I need a 10 speed rear mech?