I would say it all depends on the size of the job, quality of the lead and the chances of closing.
Is the lead going to just you of you and 6 others?
There are lead generation companies out there that are good and there are some that are not.
I used one several years ago that generated poor leads. The one project I got, about paid for the leads generated by them. In a wash situation like that, it was not worth it.
They have changed their name and keep calling me to sign up again. I am hesitant and have not.
Good networking and targeted advertising are probably better at lead generation than they are.
That said, If it is a quality lead and you can close half or a third of the leads produced, price that overhead into the job. If you close 50% add $400 to each bid for an advertising overhead to cover that. if you find out that it is only a third , add $600 to the job cost. It has to come from somewhere and it should not come out of your profit. In reality the lead generation company is a part of your salesforce and the fee for the lead should be looked at like a commission that you pay them, just as you would a salesperson that you employ.
I do not use a lead generation company at this time. I do use relators, and if they bring me a job, they get paid a commission.