Although its easy to make the assumption that mail armor was more expensive than linen armor, I'd caution against relying on this without sources. A linothorax, if made the way modern re-creationists have modeled, is not necessarily very cheap. Cloth requires a lot of work in the ancient world, and a good linothorax requires quite a bit of it, glue, and possibly some specialist knowledge.

Even if mail remained more expensive than leather or linen armor, if it was slightly (or significantly) more effective than other armor types, the cost differential was probably narrowing in our time period as iron-mining, casting, and smithing became more common.

From another perspective, I expect (but this is yet another assumption) that mail armor lent itself more easily to a centralized production model than linen armor, as casting and smithing industries tended to be concentrated near iron deposits. So that even IF mail armor was more expensive than linen or leather armor it would still be (from an organizational stand-point) easier to procure for professional armies whose equipment is procured by the state in bulk (Marian armies, possibly some later Hellenistic elements, possibly some of the Carthaginian armories). There were probably some situations where cost and effectiveness were lesser concerns than the sheer ability to procure sufficient equipment.