Just started myself and brought a good established round for £6000 and it was £3100, it was established for about 4 years, longer it's been going the more they seem to want. Make sure you go out with the guy and meet people, possibly when he's collecting so you can see the work and the amount paid and you know the location of all the work.
When I started I leaflet dropped them and informed the customers I was taking over from the last guy and if they had any concerns or questions to call. This prevented me losing customers.