On reflection 4 x monthly is pathetic lets break this down.
£10.00 job takes 3x as long first clean, To canvas is 3x the clean price, To evolve the round to almost door to door is 3x to 5 x the clean price plus the good will. Your looking for very low quality work and thats not my game.
Break down.
First clean costs £30.00
Canvass costs £30.00
Evolve round costs £40.00
Good will costs £40.00
Were now 14 x the work value. = £8,400
Window cleaning like any other business has a value and that value is not the work per month but the profit margin and were not talking working out the back of your car with no insurance and cheap gear.