All Inclusive holiday to Tunisia flying from Manchester, 18th July for 1 week, 2 adults ?

Hi, I have booked a weeks holiday to the Tej Marhaba in Tunisia, all inclusive for 2 adults with Thomas Cook on the 18th July 2012. I am unfortunately not able to go and need to sell the holiday. I will go with you to Thomas Cook and do the change of name and address. I paid £900 for the holiday a couple of weeks ago and am looking for £600 or you can make me an offer. Thanks Chris