We have a starting price of 24- for the first 1 to 4 panels ...so 1 panel or 4 its 24.....then a sliding scale upto 40 panels+ seems to work.
It is worth noting that if you do your homework and investigate why having them cleaned is beneficial to the homeowner you are then able to be armed with the right information to sell them this service.... It is one of the only services that we as w/c sell that can have a daily/monthly/yearly impact to the customer in their pockets.
When we do insides we also market a "finance, economy, cash" clearing service.
This also has a marked effect on their finances, especially if they're not in. It usually comes as surprise when they open their next credit card statement or open kiddies piggy bank to find they've been relieved of all of their available readies.
A highly profitable yet risky add-on, as yet unadvertised on the website.