Just been to Tesco Wigan and they had a huge stand of Airwick Plug In Lavender unit & refil (Normally £6.13 at Tesco) for £1.50 and on buy one get one free. Thats 75p per item! Signage says offer is on until 22nd March and sales assistant said its nationwide.
This is the large "80 days of fragrance" version.
Also available on the christmas berry candles (normally £6) on £3 each and BOGOF.