zero
It's just a lead, that's all and the chances are the individual has contacted numerous cleaners for quotes. Therefore it's not truly an investment but a waste of money buying.
How is this any different from someone contacting you through lets say for example a flyer. Even when your advertising with flyers you still have a Cost Per Call. So why do you think these leads have zero value?
No offence buddy but your coming into an industry which you have no experience in and so far just theory or as u put it, market research.
I respect your trying to earn so you can get yourself up and running, but you are asking and so expect varied answers.
The difference is because if I invest in flyers etc, it is my design, my prices and I will target areas I want to work in and so that is worth my investment on the return I make from it.
Whereas, you asking for a payment per lead, which does not mean they will agree to the price I wish to set, and has been set up through another company which they contacted and so I have zero input in those stages