Knowing how much you like chocolate, I am sure you will want to stay few days in Oaxaca. I want to recommend you the hostel where I stayed. It was the cheapest listed in Lonely Planet so I went for it even if it was quite a long walk from the bus stop and I did not regret. Prices were really fantastic-80 pesos per night in dormitory room-separated sexes. Hostel showers have warm water-very often. They are clean but sometimes a bit broken. Hostel has a big patio with chairs where you can either sit and chat with others or dry your clothes on the trees.
There is also a kitchen kind of equipped with salt available for everyone. You don’t really need to cook; straight in front of the hostel is normally sitting a lady selling Mexican tortilla filled with meat for few pesos. A Really good deal. If you want proper food, you can walk toward the market and buy something there. Plenty of cooking stalls with tables around. We had chicken with Oaxaca mole ad it was delicious. You can eat as many tortillas as you like, just clap your hands and the tortilla lady brings them for you. And believe me you will need many if you want to eat all that spicy food.
If you want hot chocolate but not spicy hot--just proper hot chocolate--have it in some of the chocolate serving places around the market. I promise you will love it. I loved it and I don’t even like chocolate!
Staying in Oaxaca is really a good deal. Planty of old ruins you will like but you can go also to some other places. I went to see the 2000 years old tree in Tule (don’t confuse it with Tula - archaeological site near DF) and also went to bath in hot waters above sulphur waterfall called El Hierve agua-boiling water. The name comes from the white crystals of sulphurs forming the waterfall not from the real water temperature. I was a very nice trip. Done by car of someone I met in the hostel together with 6 other people. The hostel has a really friendly, relaxed atmosphere, so you would love it here.