I started running about a month ago, and realise my old trainers are probably too knackered to carry on without hurting myself. I run mostly on pavement, and am starting to feel it in my knees. Can anyone recommend a good pair of supportive trainers that I could wear out and about too (so not too crazy) and that aren't too expensive (as I'm still liable to give up any minute, despite my best intentions!) Does £40ish seem reasonable?