State fee caps: many states cap the actual "notarial act" fee (often $5-$15 per stamp), the rest of what you charge is a separate, uncapped travel/service fee, which is where most of the income comes from.
Loan signing vs. simple notarization: certified loan signing agents (who walk clients through full mortgage document packages) command significantly more than a single power-of-attorney signature.
Travel distance and time of day: after-hours, weekend, and long-distance appointments typically carry a premium.
Certification: Notary Signing Agent (NSA) certification and background screening (required by most title companies) opens access to the higher-paying loan-signing work.
Starting out vs. established
New mobile notaries often start with simple single-document signings in the $25-40 range while building local relationships. NSA-certified signers doing full loan packages for title companies routinely earn $75-150+ per appointment once established, since loan signings take longer and pay accordingly.
Getting paid once you've set your rate
Most mobile notary work is paid on the spot or invoiced to a title/escrow company. Either way, a clean invoice that separates the notarial fee from the travel/service fee keeps you compliant with state fee-cap rules and makes your pricing easy to defend if ever questioned.