Cost per lead is the only number that lets you compare six channels on the same page. It is also the one most often quoted without saying what counts as a lead.
Define the lead before you measure it
A newsletter signup and a booked consultation are both called leads, and they differ by an order of magnitude in value. Before comparing anything, agree what counts: a form submission with a real phone number, a call over thirty seconds, a booked meeting. Write it down.
Half the arguments between clients and agencies in this market are two people using the same word for different things.
Category matters more than channel
A lead in real estate, legal or private healthcare costs multiples of one in a niche B2B category, on every channel. The variation between categories is far wider than the variation between Google Ads and social within a category.
This is why benchmarks copied from a US blog post are useless here. Your only meaningful benchmark is your own number last quarter.
How the channels typically behave
- Google Ads: highest intent, highest immediate cost, most predictable. Flat over time.
- SEO: nothing for months, then the lowest cost per lead you will see. Falls over time.
- Paid social: cheaper clicks, lower intent, heavily dependent on creative. Volatile.
- Email: cheapest of all, but only works on an audience the other channels built.
Which is why the split matters more than the choice.
Set a ceiling and manage to it
Average order value, multiplied by repeat rate, multiplied by gross margin, divided by close rate. That is the most a lead can cost while the business still makes money.
Every channel gets measured against that one ceiling. A channel above it either improves or loses budget to one below it. That is the whole job, and it is why the budget split should look different in month twelve than in month one.