One person in our neighborhood gets homeowners together for a deal on house washing - works out great! I'm not sure how many homeowners participate but it does get us a good price.
The lawn maintenance idea certainly has merit for the reasons you state. But I'd have to think that homeowners who are happy with the company they're currently using would be resistant to changing. 'Nothing ventured, nothing gained' - could be worth a try!
Might work easier in a brand new neighborhood, though.
Bill
