I’ve always built my bikes from scratch spec’ing all the parts. Sometimes I carry forward a set of wheels or other parts from my old bike. It’s weird but some companies seem to charge you more for building the bike and some basically give you a free groupset for buying the whole bike. It also depends on the price point.
For example: Specialized S-Works dura ace di2 - $11,000
$4500 frameset
$2500 groupset
$6000 left for wheels, bars, stem, saddle, tires??? That’s crazy.
If you had your heart set on a S-Works Tarmac of that caliber, one could hunt down a deal on a frameset, find the best deal on the group and maybe choose a $1200 wheetset to save a few bucks. You could basically have that $11,000 bike for around $8,000.
When you get to the lower tier price points then you’ll find it hard to shave 30% off. When you add it up, a $3000 Tarmac usually has exactly $3000 worth of parts thrown together.
Now, when you look at other brands like Giant or Canyon, you’ll save a lot over a brand like Specialized and you might wonder how they throw that collection of parts together for the price.