I'm trying my hardest to get this cheaply so what about this:
Take out a new HMV credit Card - 1st purchase = 10% off
Go through Quidco - 10% off
Total charge £339.99
I reckon students (with a good credit rating) could do the same in-store with their student card.
MOD EDIT - Quidco on consoles would probably be 2% only