5ten freeriders are excellent. I have a pair for when I'm riding flats, it's like having cleats almost, until you are used to them, probably feel too grippy.
Always used to get by with old skate shoes (Etnies are my preferred) but I recently bought some 'waterproof' Gelert lightweight walking shoes which cost £25 from sports direct. Can't really fault them for the money and they have proper angry treads so are very grippy!!