I stayed at Hostel Moneda last year and I was very pleased. The only problem is that you are arriving at a late hour. What I suggest is if at all possible is to grab a taxi from the airport and take it straight to the front door of Hostel Moneda. That way you could arrive safely(relatively speaking). I found the area of the Zocalo to be fairly nice and not at all dangerous, but you must be careful at all times anyways. If you take an approved airport taxi they are the best. Hostel Moneda is right on the Zocalo and close to many other important sites.
I highly recommend it, we got a private room with two beds and a bathroom for a little more than $10 a night per person, super cheap. The staff was helpful at the front desk also. PM me if you have any questions, I studied carefully how to get around Mexico City and when I got there everything went smooth with taxis and the subway, so nothing happened. If you plan on leaving early the next day for Amecameca or another city, it is very easy to get to the TAPO bus station by way of the subway which costs only 2 pesos! You have to change lines one time but the subway in Mexico City is awesome and easy to use. We also rode it with our huge backpacks and no one bothered us at all. I would expect you would have the same experience if you went and kept a cool head(it is intimidating to ride the subway there). Also if you have the money you could call for a taxi from the Hostel Moneda to take you to the TAPO, the only problem is that a market is set up every morning around 7:30 AM directly in front of the hostel in the street that prohibits the taxis from getting there, so you would have to leave around 6:00 AM to have a taxi come straight to the hostel. In my opinion, if you leave very early, take the taxi because the subway might not be running that early. If you want to sleep in, the subway is the best way because it is cheap, fast and takes you directly to the front door of the TAPO.
It isn't right next to the airport but it is a comfortable, clean place to stay with free breakfast and dinner.