"unavoidable cost" is correct and usable in written English.
You can use it in any situation where you want to refer to a cost that cannot be avoided. For example, "Unavoidable cost increases due to the pandemic have put many small businesses in financial trouble."
Carbon emissions have an unavoidable cost.
For years, the government had downplayed the severity of environmental pollution, describing it as an unavoidable cost of growth.
Negotiating these deals hurt EA's bottom line but were considered an unavoidable cost to maintain an edge over the competition.
She is spending around £125 a week on the expensive, but unavoidable, cost of storage for all her belongings.
Getting close to the sullied political leadership in Illinois was probably an unavoidable cost of winning the U.S. Senate seat.
Those electricians have a ready response to anyone who suggests that poor electrical work might be considered an unavoidable cost of war.
The aim is to end misleading promotions in which ultra-low air ticket prices are highlighted, leaving out extra unavoidable costs which travellers must pay.
He said that unavoidable costs might be considered problematic, but in the present case, he said, the plaintiffs had chosen an expensive legal theory.
Remember, it is supposed to be "insurance," a term implying that those of us lucky enough to have good health should share the unavoidable costs faced by those who have chronic health problems.
Note here that these two lie at the heart of any NC system and in a way represent unavoidable costs.
The use of numerical partial derivatives was applied to implicitly account for the unavoidable costs and component interdependencies.
