AC/DC Live: Rockband on PS3 or Xbox 360 for £7.79 at Base. Free UK delivery.
Game only (no instruments). Note that the Xbox 360 version says 'usually despatched in 4-6 days' rather than the usual 24-48 hours.
Wii owners feeling left out? It's £6.37 at Amazon UK at the moment (although their prices vary by the minute).
Thanks to goonertillidie who posted that this title was a very reasonable £8.85 @ Shopto (I just used http://www.find-dvd.co.uk
to find it cheaper).