In recent years, Quintana Roo (the state Cancún sits in) has applied a state-level visitor/tourism fee separate from any federal exit tax. Specifics — the amount, exactly how and when it's collected, and any exemptions — have shifted since it was introduced, so treat any number you read anywhere, including here, as something to verify close to your travel dates rather than a fixed fact.
The general shape of it
It's generally framed as a modest, one-time per-visitor charge intended to fund state tourism and infrastructure costs, collected either digitally in advance, on arrival, or sometimes bundled into accommodation costs depending on how the current system is run.
How to check the current details
Search for the official Quintana Roo state tourism or "Visitax"-style government page close to your travel date, rather than relying on older blog posts (including travel guides like this one) for the exact figure — fees like this are exactly the kind of detail that changes without much notice.
Practical takeaway
Budget a small, flexible amount for a possible state visitor fee on top of any federal charges, and confirm the collection method (app, kiosk, or bundled into your stay) once you're closer to departure.