What does it actually cost to set up marketing properly?

The reason nobody gives you a straight number is that "marketing" is two different purchases wearing one word. Separate them and the budget question suddenly has an honest answer.

Why can't anyone give me a straight number?

Because most answers quote the spend and ignore the setup, or quote the setup and ignore that it's worthless without a channel to run through it. A founder hears "$5k a month on ads" and funds it, then wonders six months later why they can't tell what any of it did. The money wasn't wasted on the wrong channel. It was spent before anything existed to measure it. A real number covers both halves.

What are the real line items?

Three, and only one of them is the one people forget:

• Tools and CRM. A modest monthly software cost, a CRM and a couple of connected tools. Smaller than most expect.
• The build. The scoped setup: a clear customer profile, CRM configured, source tracking, a content or distribution channel, and reporting. This is the line most founders skip, and the one that makes every other dollar measurable.
• The spend. Ads and distribution. This should be the last money you commit, not the first, because it's the only line that's wasted if the other two aren't in place.

Tie every dollar of the build to a deliverable you can point at. If a cost can't be attached to something that will exist and work when it's done, question it.

What about the "11% of revenue" rule?

Ignore it at your stage. Percentage-of-revenue benchmarks describe mature companies with established engines. For a firm that grew on referrals and is building the engine for the first time, the rule gets it backwards: you fund the infrastructure that makes spend measurable first, then scale spend against what you can actually prove works. Spend follows proof, not a percentage.