That's difficult to say as I tend to use one pair of trainers for pretty much everything (everyday use, training and hiking). Saying that, I'll buy a new pair of trainers every 18 months or so (at a guess).
My current shoe is a Hi-Tec Adventure that costs around 20 quid and they're about 2 years old and beginning to need replacing. I like them because they're cheap, have a reasonable grip pattern, are light and (most importantly for me) have almost zero heel lift (I like my shoes as flat as possible). They've performed brilliantly in all conditions in Brecon and Dartmoor - wet or dry - boggy or rocky and I've never had any problems with grip (not even when running with a pack in some pretty rocky areas). My feet certainly thank me for it : ) I haven't tried them in snow but I would anticipate that if I wore an additional pair of socks that they would be adequate (though as I've said, not preferable, for a start, they won't take a crampon).