CHEAP DELLS are NOT good. they are amongst the WORSE built machines you can buy, expect it to last a few years tops before it breaks
HIGH END DELLs on the other hand are good
there's a reason why yuo can take 2 laptops with the same spec but one costs twice as much as the other... there's more to PCs that justa spec sheet.
ps the "if its more expensive it's better" rule isnt always true, just look at Vaios