I didnt see this as a typical gd how do I whipe my butt thread given there is such a wide range of prices with coats that there must be some reasoning behind it! I generally think you're more likely to get decent advise on a forum like this than from a sales monkey doing one day a week trying to push me to the highest margin coat.
There are lots of reasons behind price differences.
More expensive jackets will generally (discounting some manufacturers "lifestyle markup") have more techincal features on, such as extra zips, padding, cords and generally "better" fit along with better materials (so more breathability/waterproofness/weight). What you want/need when walking in the mountains, skiing in conditions of -10 etc but overkill when walking to the shops in the UK 99.9% of the time.
There's no point getting a Changabang (for example) for that, you're much better off just going to a shop and looking at the basic gore/pertex/eVent jacket that looks nice, fits ok and is within your price range. None of which can really be gathered from a forum of people with different body sizes, budgets and style choices.