I used to pay £100/month for leads for my limo business, I used to get 150 -200 /month, these same leads were sold to 5 or 6 other companies in the same city so all things being equal if every enquiry actually booked I could potentially gain 30 jobs a month, however most people shopped on price ,not everyone booked, and it could be 10 hours until I got the chance to respond. 2 or 3 jobs a month were booked by me , making it an expensive marketing method.
It may be different for the CC business , though I doubt it.