You can't be any more central than this -on the Zocalo. Hotel is probably 3 star standard with price to match. They add taxes to the quoted price so a run of house room is about $78. My room was in the old centrral wing. It was huge with 20 foot beamed ceiling and a very large bathroom with separate shower/wc. As it was over the kitchen, it was hot and had no aircon or fan, but opening the windows onto the central courtyard let in some cooler air. However the dining area was below and setting up for breakfast made noise until about 11pm.
Not sure how the newer rooms in separate wing might be, but Expedia gives you run of house so you have no choice.
Eat all your meals out - it will be much cheaper and there are dozens of choices within a minutes walk. The cafe on the east side of the Zocalo is great for people watching and you can write your e-mails while having coffee.
A must is the trip to nearby Indian villages - really interesting. Take the tour offered by 'Alex & Raul' at the front entrance of the cathedral off the Zocalo every day at 9am (departs 9:15, returns 2:30; $25).
