(1) Except as provided by Subsection (2), the proper money of the claim is, as in each case may be appropriate, the money:
(a) regularly used between the parties as a matter of usage or course of dealing;
(b) 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
(c) in which the loss was ultimately felt or will be incurred by a party.
(2) The money in which the parties have contracted that a payment be made is the proper money of the claim for that payment.