Great Britain #570, 573 1/2d Orange and 2d Light Brown Queen Elizabeth II, 1958-67 Wilding Issue, Multiple Crown Watermark, A Combination Usage on a Very Fine Paquebot Cover Sent From Portugal, July 9, 1962
A very fine cover to Southgate, London, sent from a British ship sailing in Beira, Portugal on July 9, 1962, or possibly September 7. Franked with a single 1/2d orange cream paper and 2d white paper Wildings, paying the local 2.5d rate.
Our estimate of the value of this cover based on the above factors is $5. To understand how we have assessed the cover and arrived at this estimate and to gain a broader understanding of postal history collecting, I would suggest you read the article linked here. It should clarify the factors that make covers, and this one in particular scarce, and will help you to understand why we have estimated it at this amount.