These are around £30 instore in Currys. Got one my self and is about the cheapest place I could find it. It does not give the option on the PCWorld website to collect them instore otherwise they would be £9.97 with out delivery. But it may be worth giving your local store a call just in case.
10" DVD Case - Portable Case
Built in jack - Dual Jack
Use In the Back of Car - Ideal for the Kids
Adjustable - Movable strap