The only problem is that you have to ask yourself the question, do you get what you pay for? and yes, of course you do, to some extent, because when you compare the buying power of some of the retail giants, and therefore their ability to offer you products at great prices, it all becomes a bit confusing.
I'm talking about brands such as Uniqlo, which has a very good cashmere range, although not all of it is online (don't ask me why, I haven't a clue)and department stores such as John Lewis and House of Fraser, who all have their own brands. Then there are the indepdent retailers where some or all of the collection is cashmere, including Boden, Brora, Pure Collection and Crumpet England.
You can shop until you drop from any and all of these, spend incredibly reasonable amounts or a small fortune. Cashmere is always a treat, and great cashmere will last for years.
Daily Update: Yesterday was a very, very strange day (for me, anyway), starting with having to sit on the floor on the train (because I was definitely not going to stand all the way in to London, although one female told me she thought I should get up, which I thought very funny - do you take up two spaces for standing people when sitting down? Well this was a non stop train so I wasn't worrying).