Lidl will have these heated car seat massage cushions instore from Thursday 16/01/14 for £17.99 which seems reasonable.
Product Information :-
8 massage programmes with optional heat function provide soothing comfort and warmth to shoulders, back and thighs
Easy to use control panel with backlit LCD display
Ideal for in the car, at home or in the office
Includes 12V connection and mains adaptor
3 year manufacturer's warranty