1. Notwithstanding the provisions of any other law, the time price differential included in a retail installment transaction on any motor vehicle without regard to the year model designated by the manufacturer, the retail seller may charge, contract and receive any time price differential agreed to by the retail buyer, expressed in the contract as a percent per annum that shall apply to the contract regardless of its repayment schedule.

2. The time price differential shall be computed on the principal balance as a percent per annum. A minimum time price differential of twenty-five dollars may be charged on any retail installment transaction.