Considerably more than that. You need enough propellant to fuel the tanker for a trip from the lunar surface to LEO with a load of propellant, and then back to the lunar surface empty. For the tanker itself, that's roughly as much total delta-v as launching to LEO from Earth. In the hypothetical "Mars as stepping stone" scenario, you'd burn most of the propellant you produced delivering propellant to the Mars vehicle. And that's only after burning more than enough propellant to establish a Mars colony to deliver all the needed mining and refining equipment and propellant tankers to the moon.
Refueling on the moon isn't a way around this: you need to get the spacecraft, supplies, and personnel there first, which takes more delta-v than sending them to Mars and would require first refueling them in LEO or launching them from Earth with enough propellant to go straight to Mars.