Poole bay I am in your area and you should be looking at £75 as an absolute minimum not including any balconies, unless they are the Juliet type, then add more for them. This is assuming its monthly add more if not.
As for cleaning any balconies it amazes me the amount of people I see still doing them by climbing off of ladders over balustrades etc. A practice we used to use often in years gone by, but this is now in complete contravention of the working at height regulations, unless you have some kind of certified fall arest system installed that protects the worker from falling when he steps off the ladder!
So get in the habit of not offering this as customers can do this themselves safely from the inside, or offer to clean them only if internal access is given, which is rarely easy to organise amongst many flats. Good luck