Practice taught me that that "should" is doing a lot of heavy lifting here and it's often not the case, even across long time periods (years) that should allow competitors to emerge.

For example I calculated the cost of a solar install to be approximately: Material + Labour + Generous overhead + Very tidy profit = 10,000€

In practice I keep getting offers for ~14,000€, which will be reduced to 10,000€ with a government subsidy and my request for an itemized invoice is always met with radio silence.