I can confirm that there are vacancies for both our September and October Berlin-Dresden tour. It is also possible for you to arrange your own transport to and from Germany if you would like to spend some extra time there at the beginning or end of the tour. In such a circumstance we would offer you a £100 discount off the base price of the tour i.e. £689 for the September tour, or £639 for the October tour. Please note, however, that if you decide to take this option that you have to make your own way to the first hotel, and that we cannot provide ATOL protection for the tour package (since there are no flights involved).
Another possibility is for you to take the tour at the price advertised, but just use one of the flights and stay longer on either end (personally I'd recommend flying out with us and returning under your own steam). However we wouldn't be able to offer a discount in this situation as we would still be buying both sets of flight tickets, although you would be ATOL protected and would have the airport transfers included.
I hope that answers your questions, though if you have any other queries please don't hesitate to post them either here or give our team a call.