We are going on the Monarch next month for a quick getaway and DH is just going to wear black dockers, dark gray long sleeve shirt, black tie and black shoes. We've done this cruise before and he will be fine. I would suggest buying a dark long sleeve shirt and tie. He can wear it again taking you out to dinner at home.
You could try a local thrift shop/consignment shop. Our oldest son found 2 Brooks Brothers suits there for only $12/each.