Sainsburys are selling the TomTom One Classic Limited Edition UK & ROI for £50.
I bought 6 of them (in Surrey about 2 weeks ago but have been on hols!) for mainly friends and houesemates, and would post the receipt if my camera phone was a bit better.
They were not on display, but inside the cabinets that they keep all the MP3 players/phone/satnavs - so maybe just ask if they have any in stock.
The box they come in is cube in shape and scans at £50. The next nearest price is about £100.