£5k is too low. I'd budget at least £5.5k.
But once your spending £5.5k you may as well go the whole hog and have the AD experience and get a new one for a few hundred quid more, especially as you can get interest free credit and spread the payments.
Get yourself on the AD waiting list.
Back in 2011 when I got mine I had to wait less than one month. Now with the whole Rolex hysteria it appears waiting lists are longer.