Double your prices at the very least, and then charge extra for the conservatories! These kind of properties often have trouble getting a window cleaner so are usually prepared to pay a good price. I always work out a good price and then add some more, if they refuse the price you can always drop to the original price you worked out, these kind of people do not mind haggling if they need to. If you carry on quoting low prices you will regret it big time in a few months time! I was quite lucky when I first started as I built my round part time as I was doing a job where I worked shifts so had plenty of spare time to clean windows, and the good thing was that it didn't matter to me if I got the work or not so I priced high, and I was surprised to find that more often than not I still got the work
If everyone accepts your prices you are much too cheap! When I quote now I only expect to get about half of the jobs I price up, this is good as I only take on very well priced work, and after the first clean they are usually so pleased that they do not mind paying the extra!