Why is a third rate's cost difficult to state?

How much did a third-rate ship of the line cost?

There is no simple comparable figure because dockyard labor and long-stored materials were accounted separately, while guns and fittings might dominate the visible ship-specific cost.

Historical cost comparisons depend on what the accounts include. Royal dockyards employed standing workforces whose labor was not necessarily charged cleanly to one hull. Timber could be bought and seasoned long before construction, while guns and fittings entered through other accounts. A merchant ship's public purchase price and a naval estimate therefore measure different bundles of resources unless the accounting boundaries are reconstructed.