Where to buy new walking boots (UK)

In two weeks time I am walking Ben Nevis and so for the past 2 months i have been wearing these boots in order to wear them in before the big day sportsdirect.com/gelert-horizon-ladies-walking-boots-186155?colcode=18615526

However when i looked at the soles of them today I noticed that they are virtually worn out!! lol

Does anyone have any ideas of where i can get a decent pair but on a very tight budget, I have a budget of £35. I noticed on the website there are a few different brands that are within my budget also. Im very tempted to buy the same ones again as although they didn't seem to last they were very comfy and a good fit (Im a half size which makes it even harder to find boots that fit) . Any advice would be appreciated