Halfords currently have up to 50% off all their sat navs, and a further 10% on selected TomToms.
My Dad currently has a Garmin Nuvi (can't remember the number). He's a complete technophobe and really hates learning how to use gadgets. But, he loves the Garmin unit (it's one that has full Europe mapping, 'cos he needs it for work lol). It should have been about £230/£240 ish, got it in Halfords for £120. Quick looksee round online showed that to be a pretty good price (at the time) for it.
I'd strongly recommend looking at Garmin. They are pretty easy to use, and as my Dad has proven, fool proof!! And, as a plus, it hasn't tried to lead him down any footpaths/off cliffs etc etc lol