I tried Boots own, and they were ghastly, hurt my feet, cost a bomb, couldn't walk in them, forget about run in them (wasn't running at the time, just wanted my feet to stop hurting).
Second try was a podiatrist, who provided nice comfy ones which I now run in, I think about 40 pounds, not sure, as the price was part of the bill including the assessment. My feet still hurt - not when I run, but at night. No idea whether this is because they are still not right, but..
I have not had any knee trouble to speak of, and that is what I am really keen to prevent.
I'd say go for good advice. Yes, it costs, but look what you are saving.
Marj