If you are not sure about a price for a job, you should always go in higher, just in case. if you've quoted low, you are stuck with a loss, which is not good. And it doesn't look very professional if you try and put it up after three cleans. I quoted for a similar, but smaller house, and made a cut-down squeegee for the job. I realised after a couple of cleans that I was overcharging, so after twelve months dropped the price by £5, saying that some of the cost was towards my time and effort making the 'special' squeegee. That did me a lot of good.