I totally agree with you NF. To me an "all-rounder" is a horse who is capable of doing a little bit of everything even if just to a low level, so I think most horses who have been trained properly can be described as all-rounders, or potential all-rounders if still very green. You shouldn't have to spend a fortune to get a horse who can do 3 gaits in an arena, pop over small jumps and hack out without being stupid. Those are just the basics IMO, we have our youngsters doing that 6 weeks into their ridden career... As far as I'm concerned the vast majority of physically sound 8-year-olds, even if not backed until 5 or 6, should be able to do a Prelim dressage test and jump 2'6'', I don't see that as something you should need to pay extra for. £3000 to buy a horse with what I consider to be the basics is just madness IMO. Yes, maybe if you were looking for an established competition horse with a really good record - but for your average horse I should think it perfectly possible to find an 8-year-old all-rounder for £1400 if you are willing to be flexible on the less important things like height and appearance.
As for good manners, again like NF I think those should be expected of all horses regardless of their type/experience etc, why should good basic manners raise a horse's value by £1000 plus? And even if there are some manners that need working on, well unless you're talking about a serious attitude problem then you should be able to improve them fairly quickly with correct and consistent handling. Why rule out a £1500 horse whose manners need a bit of work but who ticks all the other boxes.