Cost of Vacant House Leads

[Bill S.]

Ok so I've got a friend whose step son is in a business where he knocks on doors each and every day. He sets appointments for his boss to come in and make the pitch. For every appointment he sets he gets paid $55. I am wanting to use him to scout for vacant properties that I would target with a direct mail campaign. What is the going rate in your area for vacant house leads? Trying to figure out what would be reasonable to offer without insulting but also not go broke. Is this approach even worth it? Thanks.