An item of clothing worn by lead singer Freddie Mercury, perhaps on stage or in an important pop video, is worth much more. Freddie's shades once sold at Bonhams for £800.
There is a big market for Queen memorabilia and your item is a small but still quite special little memento. As you still have the competition details, this makes it a bit more attractive to a fan. If you offer it on an online auction site you might be able to make £300 or more.
http://www.mirror.co.uk/advice-old/money/treasure-hunter/2009/07/05/james-breese-answers-your-collectables-questions-115875-21497055/