Hi Aaron, Groundy is right; getting customers is your priority, and price them properly. If you go cheap because you think it'll give you an advantage in getting them, you'll make a mistake that may take a long time to recover from.
Unless you live in some poor deprived place (like Scotland), you should try to have a minimum price per job (within reason and common sense) of £10 (though someone will be along later saying they won't get out of their van for less than £5K

). £1 a window works well as a very rough guide, but again, some common sense is needed.
And as soon as possible, go WFP. It's quicker and easier; you can work faster for longer which equals more of the 'orrible green stuff.
Also, just out of interest, which part of the country do you live in?