Having my gait analysed (two different places) helped my running and stopped my injuries completely. I guess all the top/elite athletes who have seen improvements using gait analysis wasted their time?
In my case I believed a salesman who 'looked' at my feet and sold me the completely wrong shoe - even though it fit well and felt comfortable. I then went through weeks of pain and injuries.
I now wear completely different style of shoe and run faster and injury free.
I don't think you have been ripped off - certainly not the prices Sports Direct charge. Sports Direct operate by selling low end/model shoes, or models that are 'end of life'.
For a beginner doing a 5k almost any shoe would do. I once ran a 10k in a Rockport dress shoes to show how comfortable they were.
If you are serious about running you more than often get what you pay for. I like many other regular runners would not buy from Sports Direct, but a 'real' running shop. It's also worthwhile (again if you are serious) to get your running gait analysed by the shop.