(a) The money in which the parties to a transaction have agreed that payment is to be made is the proper money of the claim for payment.
(b) If the parties to a transaction have not otherwise agreed, the proper money of the claim, as in each case may be appropriate, is the money:
(1) regularly used between the parties as a matter of usage or course of dealing;
(2) used at the time of a transaction in international trade, by trade usage or common practice, for valuing or settling transactions in the particular commodity or service involved; or
(3) in which the loss was ultimately felt or will be incurred by the party claimant.