Halfords are selling off a range of ex-display Satnav's in my local store (Uxbridge).
I asked at the counter if this was a national thing and the sales assisant seemed to think it was.
Stock will obviously vary considerably. I managed to pick up a Medion 510T for £20, sold as seen without a bracket, software or charge lead.
They had about 10 others to choose from all varying in price.
Might be worth a look.