I absolutely agree with Paul's post above so long as you know that you are going to keep walking. If you are really just starting out I would say go to Sports Direct, take some walking socks with you, and buy some Karrimore fabric boots for £40. Once you've done a few walks and decided that you are hooked then invest in a good pair of boots and use the Karrimores for walking the dog.
I love my Meindl boots but what suits me may be agony for you.
I did the same started off cheap not wanting to spend serious money thinking £100 for a pair of boots no way and i didnt know if it was a fad or something i would take up as a hobby
As my walking got more serious and longer duration i was wearing out/splitting cheap boots really fast, started to spend a bit more and wore them out as well and eventually invested in some Meindl and eventually heard about Altbergs as ive wide feet and havent had to buy any other boots for over a year now. You really do get what you pay for with all walking gear but you can find the odd good pair here and there that suit your particular style of walking and are cheap, the trouble is you generally dont find out how good they are until youve bought and used them.
True about the going to the shop and getting a fitting, once youve found your boots why not buy them from the internet? generally cheaper or if sold at Go outdoor get the price match and save some money. Dont feel obliged to buy from the shop just because they told you what size foot you are or let you try them on thats what shops are for, the internet is where to buy or use to your advantage and save money on price match to save on your hard earned cash.
Every time i go in Go Outdoors/Craghoppers etc i try on everything i would like to buy make a note of the sizes and items and then if at some point i want to buy or they go on sale at a great price i use price match if possible or buy from the internet if cheaper knowing the size and fit is good