Do custom or manufactured computers cost more

I was wondering, do self-built computers ( which cuts out the cost of labor ) cost more than computer manufacturers ( which buys parts in bulk enabling steep discounts ) ?

>>5
well depends how you see it as ripped off:
buy in a shop a hdd with imaginary price of 100 Euro: 60 Euro to (IE) maxtor 20 Euro to the guy the shopkeeper buys, 20 Euro profit for the shop (but including service if you have an good shop)
HDD in an pre build system:
(IE) Dell pays 60 Euro to maxtor makes 30Euro profit and the whole system is 90Euro (10 bucks cheaper from this part alone)
repeat for other pieces of system and look how much the big ones make out of this
also the big companies buy often OEM stuff with less waranty or low quality parts ( IE slow RAM on an Graphic-card with an good chip, because you only see (IE) GF 6800ultraturbomakespenislonger on the flyer and no RAM timing) which is even cheaper for them