Prepared to get shot down in flames on this one, but when I was in Sports Direct last week, I noticed they have started selling decent brand running shoes, e.g. ASICS, New Balance etc at reasonable prices. No good for me, as I need an extra wide fitting, but anyone who knows their requirements, could save a few quid.
However if you have any doubts follow the advice above and go speak to the experts. Running shoes are an investment, as the world is your gym and there is no subscription fee.
I didn't get my shoes from there for the reasons you have stated but I picked up a load of BARGAIN running gear: t-shirts, shorts, socks, bottle, phone holder etc. even the branded stuff is great value