I can echo the Uniqlo suggestion for price and construction quality - their denim is sourced from the Kaihara mills, all below £40.
Nudie (Regular Ralph Dry Selvedge) RRDS would fit the bill perfectly as they're a bootcut and they're a great starter jean if you're planning to get into raw denim. They're vanity sized so you need to size down one or two from your normal waist size. If you don't like the arcuates, and I'm not a fan, you can always unpick them before the first soak. Prolly about £100ish.
If money's no object, go to American Classics for LVCs, Lee Japan, Sugar Canes, Studio D'Artisan and various imported Japanese denims. Don't expect much change from £200, but the quality is unsurpassable. Cinch stock the complete current season's LVC catalogue - £150ish. There are some online outlets and proxies that will allow you to import from Japan, but it's really obsessive 'next level' shit that becomes satisfyingly addictive.