I believe the last stop of one of the downtown buses is about 100 ft from Puerto Juarez. We take the bus from the Hotel Zone to Puerto Juarez and come back by taxi. We know the ferry fare is cheaper from Puerto Juarez but you may end up paying more if you have to add the taxi fare.
Is there a reason why you aren’t taking a ferry from Playa Tortugas? You could catch a public bus in front of your hotel to Playa Tortugas. There’s a ticket counter on the street when you get off the bus. It’s closer and easier from the hotel zone to leave from Playa Tortugas. We just did this from the hotel zone a few days ago.