The danger in providing a cost breakdown is a customer who decides out of parts A,B,C,D,E decides to take parts A and C to another vendor because their 25% cheaper.
I've had that happen to me, and then was told that they'd expect B,D,E to remain the same, even though my fixed costs were the same for 3 or 5 part no's.
Needless to say I don't do any work for that customer any more.
The other danger is leaving out the cost on a particular line item, or getting the qty wrong. I quoted a set of rollers for $xxx, thinking there were 4 rollers, when there were in fact 6. My line item didn't itemize the qty, they asked for 2x the quantity, at 2x the cost. So I made 12 rollers for the price of 8, that was a $400 mistake. If I hadn't itemized each part no I could have given them a newer (increased) price and they wouldn't have caught my mistake (assuming i did)
Itemize at your peril