I have some experience of this as I sold my residential workload on the 1st March 08.
My opinion is that you may be selling yourself short on the amount you are expecting, I know the rule of thumb is to sell for 3/4 times the monthly value but you are talking about a round worth £60,000 per year.
In anyones estimation that is a sizeable business.
The value of our work was higher than you have but I can assure you without going into details that I got much more than 3 times the value.
You must have an accountant - what does he value it at. Have it valued professionally and then market the sale properly. For too long now people have undervalued their window cleaning businesses.
I worked on my round for seven years there was no way it was going to be sold for as little as 3 times its value per month.
Go and have a word with business link/chamber of commerce and let them point you in the right direction, rather than being shot down on here by those that do not know a bargain when they see one.
Rob