Why the range is so wide compared to other trades
A carpet cleaning lead and a septic tank installation lead aren't remotely comparable in scale, and the cost-per-lead figures reflect that. Routine pumping is a lower-ticket, higher-frequency service that tolerates a cheaper lead source, while installation and drainfield repair are large, infrequent, higher-margin jobs where a business can justify spending far more to win one.
Treating both under a single blended cost-per-lead number hides which side of the business a marketing dollar is actually working for, the same issue that shows up whenever a business runs meaningfully different service lines through one undifferentiated budget.
Making the math work at the high end
A $400 lead sounds expensive in isolation, but the return depends entirely on close rate and job value. At a 30 percent close rate against jobs averaging comparable value, the return has been reported landing around 3 to 1, which is a reasonable outcome for a business that can reliably close at that rate.
The risk is applying that same $400 tolerance to a lower-value pumping lead, where the math falls apart immediately. Matching lead spend to the specific job type it's meant to produce, rather than one number applied across the whole business, is what keeps this from becoming an expensive mistake. Real estate transaction referrals are a separate source worth building alongside paid lead generation, since they don't compete for the same ad budget at all.