Cheaper is skipping a step.

Code duplication and 'wrong' abstractions both count themselves amongst the other foibles of programming. But they don't directly produce a cost which can be cheap or expensive.

They produce some other high dimensional intermediate value which can then produce highly variable cost dependent on the domain, goals, and scenario.

As ever, it depends.

The depends is quantifiable, but it doesn't fit in a blog post. Think more along the lines of war and peace.