I've been in Oaxaca for about two months now, halfway through my four-month stay, and I've been avidly eating and learning as much as I can about the food. I went to two classes at Susana Trilling's "Seasons of My Heart" school and loved it, but I had one of the most unforgettable experiences of my life learning to make mole negro in a Oaxacan home with a Oaxacan grandmother. I met Senora Soledad through cooking classes at my Spanish language school, and for $350 pesos or about $35 each, my friend and I spent all day with her and her family in their home just outside Oaxaca making mole negro, from deseeding the chiles to toasting them on a comal in her outdoor wood-burning kitchen, to taking the entire mass of ingredients to the local miller to grind them to a fine paste, and then stirring it in a cazuela for an hour. The mole negro was the best I've ever had, complex, beautiful, and balanced enough not to need much sugar. As Soledad told us, you can't begin to appreciate mole negro until you know what it takes to make it. It's a rare thing for a tourist to be able to spend time with a Mexican family in their home, and Soledad and her family welcomed us like we were old friends. (I wrote a more extensive description of the class for my blog. I'm not promoting it, just want to let people know if they want more information.)
You have to speak some Spanish, but Soledad is used to teaching people who are just learning and knows the English words for all the ingredients, and she also speaks very clearly. I imagine if you wanted to learn something simpler with less expensive ingredients, the cost might be less. If anyone is interested, please contact me by the email address on my profile, and I will give you her phone number.