Some will tell you they are of substandard build quality to more expensive boats of the same size , but if you think about the price of cars a ford and a mercedes can be the same size but with a canny difference in the price ..... and the mercedes might not have as much standard kit.
Same applies to boats , the manufacturers build to a price level they want to compete at. I looked at loads of different boats including quicksilvers , some brands are really well finished and plush looking , some are really badly finished , rough and cheap looking. Quicksilvers look well priced for the quality of finish you get with them , the 640 pilothouse was on my list of contenders when I was searching.
Whether the engine is inboard or outboard is only relative when you compare like for like , I'm told Arvors are the same hull as the quicksilvers (QS640 = Arvor 215 ? ) , the Arvor 215 with a diesel inboard is about £10k more than a qs 640 with a petrol outboard , so you would need to compare the price of a qs 640 with something like an oqueteau 615 and compare the arvor 215 with something like an ocqueteau 625 to get a better price comparison.
The only way to really see what makes one boat cost so much more than another is to look at them side by side , even then you might struggle to see where the extra money has gone or been saved with some comparisons.
Ray
