(a) A bill of costs shall be filed in the case and, upon allowance, included in the judgment or decree.
(b) Before any bill of costs is taxed, the party claiming any item of cost shall attach thereto an affidavit, made by himself or by his duly authorized attorney or agent having knowledge of the facts, that such item is correct and has been necessarily incurred in the case and that the services for which fees have been charged were actually and necessarily performed.
(c) Costs which a party is entitled to recover must be taxed, whether or not they have been paid by such party.