Well most of the shops have closed, so your options are limited. Try phoning your local Asda to see if they've got the Nokia 6300 in stock. They sell it for �97.00 but it's on a cheaper tariff than Vodafone. (8p per minute to any UK phone, landline or mobile, 4p per UK text, web browsing 20p per Mb)
Or try Tesco. They sell that phone for just �79.97 (on their own calling plan, which also offers good value).
Even better might be Sainsbury's. At one time they were selling that phone (on Vodafone) for �49..99, but I don't know whether they still stock it.
Chris
PS: I'd never consider looking for a mobile phone in a Vodafone (or Orange, or whatever) shop. They're run by independent traders who simply pay a franchise fee to use the phone company's name. Many of them of them neither know nor care about what they're doing.