An eight or nine pound house should be £12 - £15 with a conservatory,Fez, I think you should rethink your prices if you're including the conservatory. Most of them have more glass than the total area of the windows in the house!
One lady recently asked us to start cleaning her new one, I said I'd time myself and charge her at the same rate as the house. It took just over the usual time so I asked for double. She thought that was a bit dear, and so, in a nice way of course,
I said she should get her son to measure up the glass in the house and also the conservatory and see how they matched up.
Next visit, I asked if she wanted the conservatory done - "Yes, every time, no problem" Nuff said - I maybe should have asked for a bit more!