I use the guy at the back of the car wash (old petrol station) on the Stone Road.
Whilst there are a lot of people saying that tyres are something you shouldn't gamble on, part worn one's aren't always a bad deal. Use a reputable seller that only sells named brands that have come off business vehicles that change them routinely often. I usually spend about £30 a tyre and they still look new! Been doing so all my life and never had an issue.
For what it's worth I once had a friend who paid top prices for the best tyres going... he had a blowout with a brand new tyre on the motorway the same day as it was fitted! Rare, but still happens.
I'd rather spend my money on a quality part worn than a brand new budget tyre. I'd also love to put £80 tyres on my car... but I'm a realist and know that a lot of us simply can't afford to do so.