The holder may, if the contract or refinancing agreement so provides, collect a delinquency and collection charge on a contract evidencing the sale of a commercial vehicle in an amount not exceeding Five Dollars ($5.00) or four percent (4%) of the amount of any delinquency in default for a period of not less than fifteen (15) days, whichever is greater, but in no event to exceed Fifty Dollars ($50.00), and on all other retail installment contracts a delinquency and collection charge in an amount not in excess of five percent (5%) or Five Dollars ($5.00), whichever is less, on each installment in default for a period of not less than ten (10) days. In addition to such delinquency and collection charge, the contract may provide for the payment of court costs and of attorneys' fee not exceeding fifteen per cent (15%) of the amount actually due and unpaid at the time the balance of the contract is accelerated and the entire amount thereof is declared to be due, if the same is referred to an attorney for collection. However, no such attorneys' fee may be charged or collected where the attorney to whom the contract was referred for collection is a salaried employee of the holder of the contract.