If an agency tells you they are getting your cost per lead down to forty dollars, they are telling you that homeowners are filling in your form.
It gets worse from there, because the ad platform learns. Every unqualified submission teaches it what a good prospect looks like, and it goes and finds you more of them. The number on the report improves every month while the work gets worse.
Your deals are large and they take months to close. A cost-per-lead figure cannot describe that, because it counts the wrong event at the wrong end of the process. The numbers that would tell you something are what a qualified request for quote costs you and what an awarded contract costs you, and almost nobody reports either.
Some of what fixes this is unglamorous and specific. A square-footage floor on the form. A building-type field with no residential option. A call-duration threshold before a call counts as anything. It is not clever work. It is just work that nobody does, because it makes the monthly lead number go down.
The industry sells you leads because leads are easy to sell. Nobody sells you the harder truth, which is that your best work already comes from people who know you, and that the job is to stop losing it.