I only used bottles very occasionally with ds, so didn't bother buying a steriliser, and instead sterilised his bottles by pouring boiling water into them. I've just read this article which says, "The current advice for parents is not to pour boiling liquid directly into bottles, not to microwave them or use scratched or worn ones."
I'm now wondering if I use bottles for dd (unlikely but you never know when you might need a break!) how I'm going to sterilise them, given that ds would never take a bottle which had been near Milton and I don't really want to spend out for a steriliser when it will hardly ever be used!